* etc/guix-install.sh (chk_init_sys): Detect OpenRC.
(sys_enable_guix_daemon): Install & enable the Guix daemon on such
systems.
* etc/openrc/guix-daemon.in: New file.
* nix/local.mk: Add a rule for it.
(openrcservicedir, nodist_openrcservice_DATA): New variables.
(CLEANFILES, EXTRA_DIST): Add them.
* .gitignore: Ignore etc/openrc/guix-daemon.

Signed-off-by: Tobias Geerinckx-Rice <me@tobias.gr>