Add release notes for 3.0.22 and revise release notes for 3.0.21.
Review Request #11599 — Created April 20, 2021 and submitted
3.0.22 is a small release, featuring just the Markdown regression fixes.
The release notes cover the details of that.
The 3.0.21 release notes have been updated to include the full name of
the person who reported the security bug fixed in that release, now that
we have permission. It also includes the missing packaging changes made
in that release.
Built the release notes, checking for build errors and spelling errors.