Add release notes for rbintegrations 0.5.

Review Request #9395 — Created Nov. 19, 2017 and submitted — Latest diff uploaded

Information

rbintegrations
master
0d25c62...

Reviewers

As the first official release, the release notes just provide an
overview of the integrations provided, with some blurbs and links to the
documentation in Review Board.

Built the docs and checked for build, spelling, and link errors.