doc: Improve ZMQ documentation

Summary:
Co-authored-by: 0xB10C <19157360+0xB10C@users.noreply.github.com>
Co-authored-by: Sebastian Falbesoner <sebastian.falbesoner@gmail.com>

This is a backport of core#23471

Test Plan: proof reading

Reviewers: #bitcoin_abc, roqqit

Reviewed By: #bitcoin_abc, roqqit

Differential Revision: https://reviews.bitcoinabc.org/D17688