In Correctness Testing Doc, render --option correctly

site/dev/contrib/testing.md

 Correctness Testing
 ===================
 
 Skia correctness testing is primarily served by a tool named DM.
 This is a quickstart to building and running DM.
 
 ~~~
 $ ./gyp_skia
 $ ninja -C out/Debug dm
 $ out/Debug/dm -v -w dm_output
 ~~~
 
 When you run this, you may notice your CPU peg to 100% for a while, then taper
 off to 1 or 2 active cores as the run finishes.  This is intentional.  DM is
 very multithreaded, but some of the work, particularly GPU-backed work, is
-still forced to run on a single thread.  You can use --threads N to limit DM to
+still forced to run on a single thread.  You can use `--threads N` to limit DM to
 N threads if you like.  This can sometimes be helpful on machines that have
 relatively more CPU available than RAM.
 
 As DM runs, you ought to see a giant spew of output that looks something like this.
 ~~~
 Skipping nonrendering: Don't understand 'nonrendering'.
 Skipping angle: Don't understand 'angle'.
 Skipping nvprmsaa4: Could not create a surface.
 492 srcs * 3 sinks + 382 tests == 1858 tasks
 
@@ skipping 22 matching lines @@
 machines.  These lines are a sort of FYI, mostly in case DM can't run some
 configuration you might be expecting it to run.
 
 The next line is an overview of the work DM is about to do.
 ~~~
 492 srcs * 3 sinks + 382 tests == 1858 tasks
 ~~~
 
 DM has found 382 unit tests (code linked in from tests/), and 492 other drawing
 sources.  These drawing sources may be GM integration tests (code linked in
-from gm/), image files (from --images, which defaults to "resources") or .skp
-files (from --skps, which defaults to "skps").  You can control the types of
-sources DM will use with --src (default, "tests gm image skp").
+from gm/), image files (from `--images`, which defaults to "resources") or .skp
+files (from `--skps`, which defaults to "skps").  You can control the types of
+sources DM will use with `--src` (default, "tests gm image skp").
 
 DM has found 3 usable ways to draw those 492 sources.  This is controlled by
---config, which today defaults to "565 8888 gpu nonrendering angle nvprmsaa4".
+`--config`, which today defaults to "565 8888 gpu nonrendering angle nvprmsaa4".
 DM has skipped nonrendering, angle, and nvprmssa4, leaving three usable configs:
 565, 8888, and gpu.  These three name different ways to draw using Skia:
 
   -    565:  draw using the software backend into a 16-bit RGB bitmap
   -    8888: draw using the software backend into a 32-bit RGBA bitmap
   -    gpu:  draw using the GPU backend (Ganesh) into a 32-bit RGBA bitmap
 
 Sometimes DM calls these configs, sometimes sinks.  Sorry.  There are many
 possible configs but generally we pay most attention to 8888 and gpu.
 
@@ skipping 39 matching lines @@
 dm_output/565/gm/alphagradients.png
 dm_output/565/gm/arcofzorro.png
 dm_output/565/gm/arithmode.png
 dm_output/565/gm/astcbitmap.png
 dm_output/565/gm/bezier_conic_effects.png
 dm_output/565/gm/bezier_cubic_effects.png
 dm_output/565/gm/bezier_quad_effects.png
                 ...
 ~~~
 
-The directories are nested first by sink type (--config), then by source type (--src).
+The directories are nested first by sink type (`--config`), then by source type (`--src`).
 The image from the task we just looked at, "8888 image mandrill_132x132_12x12.astc-5-subsets",
 can be found at dm_output/8888/image/mandrill_132x132_12x12.astc-5-subsets.png.
 
 dm.json is used by our automated testing system, so you can ignore it if you
 like.  It contains a listing of each test run and a checksum of the image
 generated for that run.  (Boring technical detail: it is not a checksum of the
 .png file, but rather a checksum of the raw pixels used to create that .png.)
 
 Unit tests don't generally output anything but a status update when they pass.
 If a test fails, DM will print out its assertion failures, both at the time
@@ skipping 24 matching lines @@
 That's the basics of DM.  DM supports many other modes and flags.  Here are a
 few examples you might find handy.
 ~~~
 $ out/Debug/dm --help        # Print all flags, their defaults, and a brief explanation of each.
 $ out/Debug/dm --src tests   # Run only unit tests.
 $ out/Debug/dm --nocpu       # Test only GPU-backed work.
 $ out/Debug/dm --nogpu       # Test only CPU-backed work.
 $ out/Debug/dm --match blur  # Run only work with "blur" in its name.
 $ out/Debug/dm --dryRun      # Don't really do anything, just print out what we'd do.
 ~~~