breadcrumbs:
New documentation related to code structure should be put in Markdown. The best practices recommendation is to put a README.md file in the code directory closest to your component or code.
To preview changes to Markdown files, see //src/docs/README.md.
Please write your Markdown in accordance with Google's style guide, and attempt to limit lines to 80 characters where possible; unfortunately, git cl format will not do this for you.
After committing the patch, you can view the rendered markdown using a URL like https://chromium.googlesource.com/chromium/src/+/master/<my path>/README.md (example).
Here are some more examples to learn from.