Add deprecations section to release notes

Change-Id: Idf848b370dd7598d38a3dfd8c13b0411769e42e4

releasenotes/notes/add-deprecations-section-6b0f118fe190585c.yaml

@@ -0,0 +1,3 @@
+---
+features:
+  - Added a new section for deprecations that occur during a release

reno/create.py

@@ -52,6 +52,13 @@ upgrade:
     needs to be worded so that it does not depend on any
     information only available in another section, such
     as the prelude. This may mean repeating some details.
+deprecations:
+  - List deprecations notes here, or remove this section.
+    All of the list items in this section are combined
+    when the release notes are rendered, so the text
+    needs to be worded so that it does not depend on any
+    information only available in another section, such
+    as the prelude. This may mean repeating some details.
 critical:
   - Add critical notes here, or remove this section.
     All of the list items in this section are combined

reno/formatter.py

@@ -21,6 +21,7 @@ _SECTION_ORDER = [
     ('features', 'New Features'),
     ('issues', 'Known Issues'),
     ('upgrade', 'Upgrade Notes'),
+    ('deprecations', 'Deprecation Notes'),
     ('critical', 'Critical Issues'),
     ('security', 'Security Issues'),
     ('fixes', 'Bug Fixes'),