Make nix-bitcoin options more discoverable

[jonasnick]

Nix-bitcoin should provide an options manpage similar to man configuration.nix. Ideally, it would also work in the examples nix-shell.

[nixbitcoin]

@erikarvstedt In #293 (comment) you wrote:

It's relatively simple to make a man nix-bitcoin that shows all nix-bitcoin options in the same format as man configuration.nix.

Did you have in mind how to do it back then? I'm thinking about running nixos-option on all our options in a container, and then automatically formatting the result to a manpage.

[mmilata]

Looks like it might be possible to reuse home-manager's code for generating docs, it even lives in a separate repo: https://gitlab.com/rycee/nmd

[nixbitcoin]

This has at least been partially fixed by #429 and will finally be closed by #352