Add section "Add relevant documentation" to contributing guidelines in the manual

[DamienCassou]

Description

• adds a section "Add relevant documentation" to contributing guidelines in the manual. This should help the contributor check changes to the documentation
• adds "html-manual" and "manPages" attributes to default.nix.

Checklist

• Change is backwards compatible.
• Code formatted with ./format.
• Commit messages are formatted like

[Kloenk]

Are those the docs build with nmd? Maybe we could use this to fix the usage of nmd? (it breaks hydra and some evaluators because of import-from-derivation)

[DamienCassou]

Are those the docs build with nmd?

I think so

Maybe we could use this to fix the usage of nmd?

I don't know what you are talking about. Is there anything I should do?

[Kloenk]

Maybe we could use this to fix the usage of nmd?

I don't know what you are talking about. Is there anything I should do?

I had to deactivate the home-manager docs in my system, because I'm unable to evaluate my systems if I have them enabled. The problem is with import-from-derivation, where I'm unable to see how many builds I'm doing at the end (hydra breaks).

[DamienCassou]

What is the relation between what you are talking about and what I did?

[rycee]

Thanks, I think this was a really good idea! I've made some minor edits and rebased to master in 4ba9ced.