Update upgrade notes

Author: micafer

docs/upgrade_notes.rst

@@ -8,10 +8,10 @@ preserve the old behavior when this is possible.
 Libcloud 3.9.0
 --------------
 
-* Support for Python 3.7 and 3.8 which have been EOL has been removed.
+* Support for Python 3.7, 3.8 and 3.9 which have been EOL has been removed.
 
-  If you still want to use Libcloud with Python 3.7 or 3.8, you should use an older
-  release which still supports Python 3.7 and 3.8.
+  If you still want to use Libcloud with Python 3.7, 3.8 or 3.9, you should
+  use an older release which still supports Python 3.7, 3.8 and 3.9.
 
 * [AZURE ARM] Added a new argument to destroy_node() to also delete node's managed
   OS disk as part of the node's deletion. Defaults to true. This can be reverted by