PYTHON-3157 Update Release Documentation to Include Github Releases (#900)

Author: blink1073

RELEASE.rst

@@ -89,3 +89,9 @@ Doing a Release
 15. File a ticket for DOCSP highlighting changes in server version and Python
     version compatibility or the lack thereof, for example:
     https://jira.mongodb.org/browse/DOCSP-13536
+
+16. Create a GitHub Release for the tag using
+    https://github.com/mongodb/mongo-python-driver/releases/new.
+    The title should be "PyMongo X.Y.Z", and the description should contain
+    a link to the release notes on the the community forum, e.g.
+    "Release notes: mongodb.com/community/forums/t/pymongo-4-0-2-released/150457."