That's why I like documentation with the comment section. Even if something's missing, there is a good chance someone asked about it. Also comments section provides an instant feedback to people writing posts to that documentation.

While I wholeheartedly agree, you need a full-time moderation team if you want to enable comments.

And why, what do those lines mean

> Which file? And where in the file do I add those lines?

/etc/nixos/configuration.nix if you haven't structured your config differently.

> And where in the file do I add those lines?

Consult `man configuration.nix` or search.nixos.org