Adds additional handbook development docs
Why is this change being made?
This MR adds a few additional documentation notes as part of handbook#246 (closed). Sections have been added or updates for:
- Access Tokens
- Code Quality Report
- Codeowners
- Dependency Upgrades
@cynthia would you mind giving this MR a review when you have a moment? Thanks!
Closes handbook#270 (closed)
Edited by Cynthia "Arty" Ng