Add release notes for Review Board 6.0 beta 3.
Review Request #13246 — Created Aug. 29, 2023 and submitted — Latest diff uploaded
This is a large beta, featuring improved visuals, a new Markdown
formatting toolbar, improvements to the Unified Review Banner, review
tips, and lots of other fixes and enhancements.
Built the docs. Checked for spelling errors, build errors, and bad
links.