Add release notes for 3.0 RC 1.

Review Request #9338 — Created Oct. 30, 2017 and submitted — Latest diff uploaded

Information

Review Board
release-3.0.x
8704020...

Reviewers

This covers the new features and usability improvements for review
request entries, extensions, patching in the API, and bug fixes for new
features introduced throughout 3.0.

Built the docs and read through them.

Checked for spelling errors.