creating printing.nix

I dont always need printing enable. this will allows me to quickly add the printing setting when i do

common/optional/printing.nix

@@ -0,0 +1,7 @@
+{ pkgs, ... }:
+{
+  services.printing = {
+    enable = true;
+    drivers = with pkgs; [ gutenprint hplip ];
+  };
+}