zmq: update docs to reflect feature is compiled in automatically if possible
zmq: update docs to reflect feature is compiled in automatically if possible

Signed-off-by: Johnathan Corgan <970c387dcb42498229f453ae092d0497276e2f9b@corganlabs.com>

wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin