acpilight: add to module-list

acpilight package and module have been added to nixpkgs, but the
module hasn't been added to module-list.nix, so using it results in
the following error.

```
The option `hardware.acpilight' defined in `/etc/nixos/configuration.nix' does not exist.
```

Add the module to module-list.nix.

nixos/modules/module-list.nix

@@ -35,6 +35,7 @@
   ./config/users-groups.nix
   ./config/vpnc.nix
   ./config/zram.nix
+  ./hardware/acpilight.nix
   ./hardware/all-firmware.nix
   ./hardware/bladeRF.nix
   ./hardware/brightnessctl.nix