Start using reno for releasenotes

It's probably a good idea to be specific about what's changing in reno
releases.

Since reno support wasn't in tree we didn't pick up notes for these two
changes, but they're things users might want to know about.

Change-Id: I249a3a4d0cf378b60bf43ce65d49416879d5517e

doc/requirements.txt

@@ -1,2 +1,3 @@
 sphinx!=1.6.6,!=1.6.7 # BSD
 openstackdocstheme>=1.11.0 # Apache-2.0
+reno>=2.8.0 # Apache-2.0

doc/source/conf.py

@@ -31,6 +31,7 @@ import os
 extensions = [
     'sphinx.ext.autodoc',
     'openstackdocstheme',
+    'reno.sphinxext',
 ]
 
 # Add any paths that contain templates here, relative to this directory.

doc/source/index.rst

@@ -11,6 +11,7 @@ for review.
    installation
    usage
    developing
+   releasenotes
 
 
 Indices and tables

doc/source/releasenotes.rst

@@ -0,0 +1,6 @@
+=============
+Release Notes
+=============
+
+.. release-notes::
+   :unreleased-version-title: In Development

releasenotes/notes/missed-notes-f903719767e0a0ce.yaml

@@ -0,0 +1,18 @@
+---
+features:
+  - |
+    Patch download now supports change urls. Rather than forcing users to copy
+    only part of a URL to a review, users may now paste the whole change URL.
+fixes:
+  - |
+    Fix git review -d M,N for newer gerrit. The "number" field returned via
+    gerrit JSON can be a string (2.13) or a integer (~2.14).
+  - |
+    Update default gerrit namespace for newer gerrit. According to Gerrit
+    documentation for 2.15.3, refs/for/'branch' should be used when pushing
+    changes to Gerrit instead of refs/publish/'branch'.
+upgrade:
+  - |
+    The ``-c`` and ``--compatible`` command line options have been removed.
+    They had been there so someone could request compatibility with older
+    Gerrits, but the need for this has gone away.