Add reviewing section to release notes doc
Add reviewing section to release notes doc

In addition to reviewing comments, the key thing here is to get
a reference to the reno doc about why you need to patch release
notes directly to a stable branch or else they show up in the
wrong release.

Change-Id: Ice4f70d56aa81d4470ef8067d572fd8294d6cd6f

mahak/cinder,openstack/cinder,mahak/cinder,openstack/cinder