a6abec9c66
system-sendmail allows all sendmail's to be auto-detected, including on non-NixOS systems. This is, to me, a better UX than having to manually override the sendmailPath argument. In exchange, it is a breach of retro-compatibility. Given right now I can't see any uses for sendmailPath other than what is supported by system-sendmail, I didn't keep it, but it'd be possible to allow sendmailPath to override the choice of sendmail from system-sendmail.
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.