This module allows root autoLogin, so we would break that for users, but they shouldn't be using it anyways. This gives the impression like auto is some special display manager, when it's just lightdm and special pam rules to allow root autoLogin. It was created for NixOS's testing so I believe this is where it belongs.
To build the manual, you need Nix installed on your system (no need
for NixOS). To install Nix, follow the instructions at
https://nixos.org/nix/download.html
When you have Nix on your system, in the root directory of the project
(i.e., `nixpkgs`), run:
nix-build nixos/release.nix -A manual.x86_64-linux
When this command successfully finishes, it will tell you where the
manual got generated.