Add ZMQ documentation to developer guides

[CryptoGrampy]

There is currently zero :wink: documentation on using ZMQ with Monerod. Would like to see this added to https://www.getmonero.org/resources/developer-guides/ that describes how to use it, and what topics can be subscribed/published(?) to. Perhaps a 'why would I use this' would be helpful as well.

[CryptoGrampy]

Was referred to this doc from someone in Monero-Dev. Would be helpful in creating a dev guide: https://github.com/monero-project/monero/blob/master/docs/ZMQ.md

I also asked VTNerd about potential upcoming additions to ZMQ in Monero Dev: maybe msgpack in addition to json - the notifications are "slow" enough it probably only matters during syncing there's also the possibility of CurveZMQ for TLS like security "slow" -> once sync'ed the number of notifications per sec is somewhat low