Update README.md
Update README.md
Allow XSUB/XPUB to send/recv messages unrelated to sub/unsub

Messages not prefixed with 0 or 1 can be send from subscriber to
publisher.
Merge pull request #145 from sofusmortensen/master

Allow XSUB/XPUB to send/recv messages unrelated to sub/unsub
Signaler using ephemeral port