Add release notes for Djblets 0.9.8.

Review Request #9023 — Created June 18, 2017 and submitted — Latest diff uploaded

Information

Djblets
release-0.9.x
738d2cf...

Reviewers

This is a small release that contains only a couple internal
packaging-related changes (which don't affect consumers) and a backport
of Django 1.8's URLValidator.

Built the docs and tested that the URLValidator link went to the right
place.