If the keyboard configuration is an empty set, don't run the setxkbmap
service.
The default values for all keyboard options are null or empty so long
as the state version is set to 19.09 or higher (21.05 being the latest
version).
Specifically, instead of
services.dbus.packages = with pkgs; [ gnome.dconf ];
we now recommend
programs.dconf.enable = true;
which does the same and more.
The docs implied that fish was not really supported, but if fish is
managed by Home Manager, the generated config does use fenv to source
the session-vars file. Update the installation instructions and FAQ to
mention that fish does work, and mention fenv in the README.
