generate manpage

Not a bug per-se but I am trying to generate the manpage for notif-send as there exists one apparently: http://manpages.ubuntu.com/manpages/xenial/man1/notify-send.1.html . If I grep the source for the description in the man, I find nothing. I've tried to build with this config https://github.com/teto/nixpkgs/commit/45f4b30f9753c1408e788c64b921f5c43e1b26eb yet I can't find any manpage.