[Docs] Emphasize the necessity of TCP for Supervisor function
The Supervisor must have UDP _and_ TCP communication channels open in
order to function properly.
The fact that our TCP communication happens to be implemented in terms
of ZeroMQ at the moment isn't operationally important.
@@ -39,7 +39,7 @@ Butterfly is an eventually consistent system - it says, with a very high degree
#### Transport Protocols
-Supervisors communicate with each other using UDP and ZeroMQ, over port 9638.
+Supervisors communicate with each other using UDP and TCP, both using port 9638.
#### Information Security
