Website with automatically generated docs from NixOS modules

[aciceri]

To be implemented after #5

Take inspiration from:

• https://nix-community.github.io/ethereum.nix/reference/module-options/geth/
• https://flake.parts/options/flake-parts
• https://input-output-hk.github.io/haskell.nix/reference/modules.html
• https://rycee.gitlab.io/home-manager/options.html

@avnik and me prefer the first one

It would be nice also having static pages generated from some markdown files.

[aciceri]

It works!