Add support for fontawesome icons in docs text

I don't know if we have a need for it,
but I am using it in another Sphinx project and I didn't want to forget to mention it here.

This is potentially useful for things like writing about UI.
(Or maybe not! We've managed so far without it...)

https://github.com/fraoustin/sphinx_fontawesome

Review the repository's Sphinx documentation setup and the linked sphinx_fontawesome project first. Clarify whether icon support is wanted and which documentation use cases it should cover; done should include an agreed integration and a successful docs build demonstrating the intended icon rendering.

Written by the indexing model from the issue text.