Add release notes for Review Board 3.0.6.
Review Request #9863 — Created April 9, 2018 and submitted — Latest diff uploaded
This is a small bug fix release that fixes compatibility issues with
GitLab, Bazaar, and Mercurial, along with Local Site URL-related issues
and links in e-mails.
Built the docs and checked through them for issues.
Checked for spelling and build errors.