+doc StreamTCP docs

It's not the same level ( looks like https://www.evernote.com/shard/s9/sh/b924c5ac-c268-4138-a2f3-04093d4ef4f0/f852a52d4985266a4434bd68bb768c16/deep/0/Quick-Start---Akka-Documentation.png )
but you're right it probably looks worse than with just `===`. I'll remove the `###` section