PYTHON-2455 Add DOCS ticket step to release checklist (#541)

(cherry picked from commit 55eef0e)

Author: ShaneHarvey

RELEASE.rst

@@ -102,3 +102,7 @@ Doing a Release
 
 15. Announce the release on:
     https://developer.mongodb.com/community/forums/c/community/release-notes/
+
+16. File a ticket for DOCS highlighting changes in server version and Python
+    version compatibility or the lack thereof, for example:
+    https://jira.mongodb.org/browse/DOCS-12644