A common problem encountered by new contributors to the project is that
the commit messages or review request descriptions aren't always
sufficient to describe the change without requiring additional
information from a bug report or diff. Sometimes they focus on
referencing bug numbers or filenames, and sometimes they don't go into
what the core problem was that the change addressed. This makes it
harder to write release notes or to scan for review requests for a given
topic.

This adds a page to the codebase documentation explaining guidelines and
tips for writing good review request and commit descriptions. It's
broken down into sections for summaries, descriptions, testing, and
general writing tips.

Built the docs and viewed them. Formatting looked correct.
Ran spell checker. Didn't see any spelling errors.