This makes a few changes:
1) Per documentation policy, lowercase project names ("ironic" and
"nova").
2) Adds a blurb about reading the release notes before upgrading, as
that's where per-version upgrade steps and recommendations are now
documented. Refers to the per-cycle upgrade steps in this guide as
"pre-release-notes" upgrade docs.
3) Adds a general upgrade process - upgrade ironic before nova, and the
steps to upgrade ironic.
Change-Id: I087bc8ffae1893ad61f1eb734fbb1a9ed236c79d
c7d95602b9