Add release notes for Review Board 2.0.26.

Review Request #8608 — Created Jan. 11, 2017 and submitted — Latest diff uploaded

Information

Review Board
release-2.0.x
28f8317...

Reviewers

This is a pretty small release that just contains some bug fixes
shipping along with Review Board 2.5.8.

Successfully built the docs.

Checked for spelling errors.