meta-issue: Improve user and developer documentation

[erikmd]

Related user(s):

@yurug, @erikmd

Related issue(s) or PR(s):

• #504
• #514
• #494

Related project scope(s):

documentation

The problem:

• [ ] @AltGr Reply https://github.com/ocaml-sf/learn-ocaml/issues/588
• [ ] @yurug Document operational semantics of constr of Learnocaml_api.request
• [ ] @erikmd Better document availability of static binaries (learn-ocaml serve pas besoin switch) https://github.com/ocaml-sf/learn-ocaml/pull/504
• [ ] @erikmd Document the procedure to fetch/use macOS binaries
• [ ] @erikmd Better document markdown-to-html (feature already in master)
• [ ] @yurug Add Markdown badges in the README?
• [ ] @yurug Mention https://github.com/learn-ocaml-community/teaching-feedback in the README
• [ ] @erikmd Improve dev. documentation (e.g., mentioning direnv, magit, git prompt…)
• [ ] Address https://github.com/ocaml-sf/learn-ocaml/issues/591
• [ ] Address https://github.com/ocaml-sf/learn-ocaml/issues/524
• [ ] Address https://github.com/ocaml-sf/learn-ocaml/issues/573
• [x] @AltGr Add documentation on the teacher board
  cf. e.g. https://github.com/ocaml-sf/learn-ocaml/issues/514#issuecomment-1412780891

Wanted solution:

No response

Considered alternatives:

No response

Additional context:

No response