Add release notes for Review Bot 2.0.1.
Review Request #11561 — Created March 29, 2021 and submitted
This is a small release with bug fixes for Python 3 and Review Board
The plan initially was to release these fixes in Review Bot 3.0, but
that release is undergoing a lot of additional work, and we don't want
to delay these fixes any longer.
Built the docs. Verified there were no build errors or spelling errors.