update contributing.rst to reflect release notes and bugs

Hitherto we have tried to enforce the requirement that changes have
Launchpad bugs. More openstack projects have moved away from this
requirement and it may be time for Trove to do the same.

We use reno for release notes and therefore if a release note is not
specified in the commit, it will not make it to the official release
notes page. We should therefore require release notes for all user
visible changes.

Change-Id: If72fc47c1d699b20a85574f5945ecff35cc0d008

CONTRIBUTING.rst

@@ -72,7 +72,8 @@ The Trove project encourages the guidelines (below).
      * The change contains content that is demonstrably inappropriate,
      * The test cases do not exercise the change(s) being proposed,
      * The change causes a failure in the pylint job (see pylint
-       section below).
+       section below),
+     * A user visible change does not provide a release note.
 
 Some other reviewing guidelines:
 
@@ -141,6 +142,34 @@ process.
    there is no available volunteer who will step up to take over the
    patch set.
 
+Launchpad Bugs
+--------------
+
+Bugs should be filed on Launchpad at:
+
+    https://bugs.launchpad.net/trove
+
+All changes that address a Launchpad bug should include the bug in the
+Commit Message using the Closes-Bug, Related-Bug, or Partial-Bug keyword.
+
+It is not required that a Launchpad bug be filed for every change.
+
+Release Notes
+-------------
+
+All user visible changes should include a release note. Trove uses
+reno to generate release notes and therefore only those release notes
+that are submitted as part of a change will be included in the release
+notes. The failure to add a release note for a user visible change
+should be identified in review, and corrected.
+
+If a Launchpad bug is being fixed, the release note should list the
+bug number.
+
+For help using reno, the release notes tool, see:
+
+    https://wiki.openstack.org/wiki/Trove/create-release-notes-with-reno
+
 Trove Documentation
 ===================