Update docs

[SirZach]

I only found out that there's a callback associated to send because of an unaccepted PR to make send promisified. Any docs around the promises or callbacks would really help new users.

[damianobarbati]

Yeah, we're in 2017 not in 90's: world is async/await'd now.

[mblarsen]

There are PRs from 2015 to update the docs — broken links. I think this repo is dead.