cc: Add link to "how cc works" doc

Change-Id: Idea90b5d7c13a961f9eeb0d144f0960f362b761f
Reviewed-on: https://chromium-review.googlesource.com/c/1357430Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612851}

cc/README.md

@@ -42,6 +42,10 @@ composited browser contents into a backbuffer or a bitmap, respectively.
 Design documents for the graphics stack can be found at
 [chromium-graphics](https://www.chromium.org/developers/design-documents/chromium-graphics).
 
+## Other Docs
+
+* [How cc Works](https://docs.google.com/document/d/1yjzOWrPfFGviEd1nru3yzqxSHETC-zsEBSt9C8SvV-Q/edit)
+
 ## Glossaries
 
 ### Active CompositorFrame