Document --zmq-external option.
Document --zmq-external option.

lgeiger/zmq-prebuilt,interpretor/zeromq.js,interpretor/zeromq.js,lgeiger/zmq-prebuilt,interpretor/zeromq.js,lgeiger/zmq-prebuilt,lgeiger/zmq-prebuilt,interpretor/zeromq.js,lgeiger/zmq-prebuilt,interpretor/zeromq.js