message: Add a link from ZMQ doc to ZMQ example in contrib/
diff: @@ -96,7 +96,7 @@ ZeroMQ endpoint specifiers for TCP (and others) are documented in the
  Client side, then, the ZeroMQ subscriber socket must have the
  ZMQ_SUBSCRIBE option set to one or either of these prefixes (for
  instance, just `hash`); without doing so will result in no messages
  -arriving. Please see `contrib/zmq/zmq_sub.py` for a working example.
  +arriving. Please see [`contrib/zmq/zmq_sub.py`](/contrib/zmq/zmq_sub.py) for a working example.
  ## Remarks
  