MANIFEST.in: include python schema delta scripts (we now have one in 20/)

MANIFEST.in

@@ -5,6 +5,7 @@ include *.rst
 include demo/README
 
 recursive-include synapse/storage/schema *.sql
+recursive-include synapse/storage/schema *.py
 
 recursive-include demo *.dh
 recursive-include demo *.py