supersize: Update README.md with technical details.

tools/binary_size/libsupersize/testdata/Console.golden

 ********************************************************************************
 Entering interactive Python shell. Quick reference:
 
 SizeInfo: Clustered, metadata, raw_symbols, section_sizes, symbols
 Symbol: FlagsString, IsBss, IsGeneratedByToolchain, IsGroup, address, aliases, end_address, flags, full_name, generated_source, is_anonymous, name, num_aliases, object_path, padding, pss, pss_without_padding, section, section_name, size, size_without_padding, source_path, template_name
 
 SymbolGroup (extends Symbol): Clustered, CountUniqueSymbols, Filter, GroupedBy, GroupedByName, GroupedByPath, GroupedBySectionName, Inverted, IterLeafSymbols, IterUniqueSymbols, Sorted, SortedByAddress, SortedByCount, SortedByName, WhereAddressInRange, WhereBiggerThan, WhereFullNameMatches, WhereGeneratedByToolchain, WhereHasAnyAttribution, WhereHasPath, WhereInSection, WhereIsTemplate, WhereMatches, WhereNameMatches, WhereObjectPathMatches, WherePathMatches, WhereSourceIsGenerated, WhereSourcePathMatches, WhereTemplateNameMatches, is_sorted
 
 SymbolDiff (extends SymbolGroup): IsAdded, IsRemoved, IsSimilar, WhereNotUnchanged, added_count, changed_count, removed_count, unchanged_count
 
@@ skipping 37 matching lines @@
 # (and feel free to add your own!).
 Metadata:
     elf_arch=arm
     elf_build_id=WhatAnAmazingBuildId
     elf_file_name=elf
     elf_mtime={redacted}
     git_revision=abc123
     gn_args=var1=true var2="foo"
     map_file_name=../test.map
 
-Section Sizes (Total=43,785,380 bytes):
-    .bss: 1,300,456 bytes (not included in totals)
-    .data: 101,768 bytes (0.2%)
-    .data.rel.ro: 1,065,224 bytes (2.4%)
-    .data.rel.ro.local: 790,024 bytes (1.8%)
-    .rodata: 5,927,652 bytes (13.5%)
-    .text: 35,900,712 bytes (82.0%)
+Section Sizes (Total=41.8mb (43785380 bytes)):
+    .bss: 1.24mb (1300456 bytes) (not included in totals)
+    .data: 99.4kb (101768 bytes) (0.2%)
+    .data.rel.ro: 1.02mb (1065224 bytes) (2.4%)
+    .data.rel.ro.local: 771kb (790024 bytes) (1.8%)
+    .rodata: 5.65mb (5927652 bytes) (13.5%)
+    .text: 34.2mb (35900712 bytes) (82.0%)
 
-Showing 48 symbols (45 unique) with total pss: 44309900 bytes
-.text=34.2mb     .rodata=5.65mb     other=2.37mb     total=42.3mb
+Showing 48 symbols (45 unique) with total pss: 43785380 bytes
+.text=34.2mb     .rodata=5.65mb     .data*=1.87mb     .bss=512kb      total=41.8mb
 Number of object files: 10
 
 Index, Running Total, Section@Address, PSS
 ------------------------------------------------------------
 0)         16 (0.0%)  t@0x28d900   16      base/page_allocator.cc
              _GLOBAL__sub_I_page_allocator.cc
 1)         72 (0.0%)  t@0x28d910   56      base/page_allocator.cc
              _GLOBAL__sub_I_bbr_sender.cc
 2)        100 (0.0%)  t@0x28d948   28      base/page_allocator.cc
              _GLOBAL__sub_I_pacing_sender.cc
@@ skipping 18 matching lines @@
 12)     75544 (0.2%)  t@0x2a0010   4       third_party/fft_float.cc
              FooAlias
 13)     75548 (0.2%)  t@0x2a0010   4       third_party/fft_float.cc
              BarAlias
 14)     75576 (0.2%)  t@0x2a0020   28      third_party/container.c
              blink::ContiguousContainerBase::ContiguousContainerBase
 15)     79616 (0.2%)  t@0x2a1000   4040    {no path}
              ** symbol gap 1
 16)     79710 (0.2%)  t@0x2a1000   94      third_party/container.c
              blink::PaintChunker::releasePaintChunks [clone .part.1]
-17)  35900712 (81.0%) t@0x24ca628  35821002 {no path}
+17)  35900712 (82.0%) t@0x24ca628  35821002 {no path}
              ** symbol gap 2 (end of section)
-18)  37866121 (85.5%) r@0x266e600  1965409 {no path}
+18)  37866121 (86.5%) r@0x266e600  1965409 {no path}
              ** merge strings
-19)  37866124 (85.5%) r@0x284e364  3       {no path}
+19)  37866124 (86.5%) r@0x284e364  3       {no path}
              ** symbol gap 2
-20)  37866132 (85.5%) r@0x284e364  8       base/page_allocator.cc
-21)  37866176 (85.5%) r@0x284e370  44      base/page_allocator.cc
+20)  37866132 (86.5%) r@0x284e364  8       base/page_allocator.cc
+21)  37866176 (86.5%) r@0x284e370  44      base/page_allocator.cc
              Name
-22)  37866208 (85.5%) r@0x284e398  32      third_party/container.c
+22)  37866208 (86.5%) r@0x284e398  32      third_party/container.c
              chrome::mojom::FilePatcher::Name_
-23)  38542193 (87.0%) r@0x284e518  675985  {no path}
+23)  38542193 (88.0%) r@0x284e518  675985  {no path}
              ** merge strings
-24)  38542248 (87.0%) r@0x28f3450  55      third_party/paint.cc
+24)  38542248 (88.0%) r@0x28f3450  55      third_party/paint.cc
              kAnimationFrameTimeHistogramClassPath
-25)  38542252 (87.0%) r@0x28f3480  4       third_party/paint.cc
+25)  38542252 (88.0%) r@0x28f3480  4       third_party/paint.cc
              blink::CSSValueKeywordsHash::findValueImpl::value_word_list
-26)  41828364 (94.4%) r@0x2c158e4  3286112 {no path}
+26)  41828364 (95.5%) r@0x2c158e4  3286112 {no path}
              ** symbol gap 3 (end of section)
-27)  41828420 (94.4%) d@0x2c176f0  56      third_party/icu/ucnv_ext.c
+27)  41828420 (95.5%) d@0x2c176f0  56      third_party/icu/ucnv_ext.c
              ChromeMainDelegate [vtable]
-28)  41828444 (94.4%) d@0x2c17728  24      third_party/icu/ucnv_ext.c
+28)  41828444 (95.5%) d@0x2c17728  24      third_party/icu/ucnv_ext.c
              chrome::mojom::FieldTrialRecorder [vtable]
-29)  42618348 (96.2%) d@0x2c17740  789904  third_party/container.c
+29)  42618348 (97.3%) d@0x2c17740  789904  third_party/container.c
              chrome::mojom::FieldTrialRecorderProxy [vtable]
-30)  42618380 (96.2%) d@0x2cd84e0  32      third_party/gvr-android-sdk/libgvr_shim_static_arm.a/libcontroller_api_impl.a_controller_api_impl.o
+30)  42618380 (97.3%) d@0x2cd84e0  32      third_party/gvr-android-sdk/libgvr_shim_static_arm.a/libcontroller_api_impl.a_controller_api_impl.o
              .Lswitch.table.45
-31)  42618388 (96.2%) d@0x2cd84f0  8       third_party/gvr-android-sdk/libgvr_shim_static_arm.a/libport_android_jni.a_jni_utils.o
+31)  42618388 (97.3%) d@0x2cd84f0  8       third_party/gvr-android-sdk/libgvr_shim_static_arm.a/libport_android_jni.a_jni_utils.o
              kSystemClassPrefixes
-32)  42618444 (96.2%) d@0x2cd8500  56      third_party/paint.cc
+32)  42618444 (97.3%) d@0x2cd8500  56      third_party/paint.cc
              ChromeMainDelegateAndroid [vtable]
-33)  42618468 (96.2%) d@0x2cd8538  24      base/page_allocator.cc
+33)  42618468 (97.3%) d@0x2cd8538  24      base/page_allocator.cc
              mojo::MessageReceiver [vtable]
-34)  42618480 (96.2%) d@0x2cd8550  12      base/page_allocator.cc
+34)  42618480 (97.3%) d@0x2cd8550  12      base/page_allocator.cc
              kMethodsAnimationFrameTimeHistogram
-35)  43683612 (98.6%) d@0x2ddc608  1065132 {no path}
+35)  43683612 (99.8%) d@0x2ddc608  1065132 {no path}
              ** symbol gap 3 (end of section)
-36)  43683616 (98.6%) d@0x2de7000  4       base/page_allocator.cc
+36)  43683616 (99.8%) d@0x2de7000  4       base/page_allocator.cc
              google::protobuf::internal::pLinuxKernelCmpxchg
-37)  43683620 (98.6%) d@0x2de7004  4       third_party/container.c
+37)  43683620 (99.8%) d@0x2de7004  4       third_party/container.c
              google::protobuf::internal::pLinuxKernelMemoryBarrier
-38)  43683772 (98.6%) d@0x2de7008  152     third_party/container.c
+38)  43683772 (99.8%) d@0x2de7008  152     third_party/container.c
              base::android::kBaseRegisteredMethods
-39)  43683776 (98.6%) d@0x2de70a0  4       third_party/container.c
+39)  43683776 (99.8%) d@0x2de70a0  4       third_party/container.c
              base::android::g_renderer_histogram_code
-40)  43683780 (98.6%) d@0x2de70a4  4       third_party/container.c
+40)  43683780 (99.8%) d@0x2de70a4  4       third_party/container.c
              base::android::g_library_version_number
-41)  43785380 (98.8%) d@0x2dffd88  101600  {no path}
+41)  43785380 (100.0%) d@0x2dffd88  101600  {no path}
              ** symbol gap 3 (end of section)
-42)  43785380 (98.8%) b@0x0        262144  third_party/fft_float.cc
+42)  43785380 (100.0%) b@0x0        262144  third_party/fft_float.cc
              ff_cos_131072
-43)  43785380 (98.8%) b@0x0        131072  third_party/fft_fixed.cc
+43)  43785380 (100.0%) b@0x0        131072  third_party/fft_fixed.cc
              ff_cos_131072_fixed
-44)  43785380 (98.8%) b@0x0        131072  third_party/fft_float.cc
+44)  43785380 (100.0%) b@0x0        131072  third_party/fft_float.cc
              ff_cos_65536
-45)  43785380 (98.8%) b@0x2dffda0  28      third_party/icu/ucnv_ext.c
+45)  43785380 (100.0%) b@0x2dffda0  28      third_party/icu/ucnv_ext.c
              g_chrome_content_browser_client
-46)  43785380 (98.8%) b@0x2dffe80  200     third_party/icu/ucnv_ext.c
+46)  43785380 (100.0%) b@0x2dffe80  200     third_party/icu/ucnv_ext.c
              SaveHistogram::atomic_histogram_pointer
-47)  43785380 (98.8%) b@0x2dffe84  4       third_party/icu/ucnv_ext.c
+47)  43785380 (100.0%) b@0x2dffe84  4       third_party/icu/ucnv_ext.c
              g_AnimationFrameTimeHistogram_clazz