document cpuid command line behavior

docs/getting_started.md

 # Getting Started
 
 How to get and build the libyuv code.
 
 ## Pre-requisites
 
 You'll need to have depot tools installed: https://www.chromium.org/developers/how-tos/install-depot-tools
 Refer to chromium instructions for each platform for other prerequisites.
 
 ## Getting the Code
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 Running tests:
 
     util/android/test_runner.py gtest -s libyuv_unittest -t 7200 --verbose --release --gtest_filter=*
 
 Running test as benchmark:
 
     util/android/test_runner.py gtest -s libyuv_unittest -t 7200 --verbose --release --gtest_filter=* -a "--libyuv_width=1280 --libyuv_height=720 --libyuv_repeat=999 --libyuv_flags=-1"
 
 Running test with C code:
 
-    util/android/test_runner.py gtest -s libyuv_unittest -t 7200 --verbose --release --gtest_filter=* -a "--libyuv_width=1280 --libyuv_height=720 --libyuv_repeat=999 --libyuv_flags=0 --libyuv_cpu_info=0"
+    util/android/test_runner.py gtest -s libyuv_unittest -t 7200 --verbose --release --gtest_filter=* -a "--libyuv_width=1280 --libyuv_height=720 --libyuv_repeat=999 --libyuv_flags=1 --libyuv_cpu_info=1"
 
 #### Building with GN
 
     gn gen out/Release "--args=is_debug=false target_cpu=\"x86\""
     gn gen out/Debug "--args=is_debug=true target_cpu=\"x86\""
     ninja -C out/Release
     ninja -C out/Debug
 
 ### Building Offical with GN
 
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     git checkout -b mycl -t origin/master
     git pull
     <edit files>
     git add -u
     git commit -m "my change"
     git cl lint
     git cl try
     git cl upload -r a-reviewer@chomium.org -s
     <once approved..>
     git cl land