add user to scanner group

modules/users.nix

@@ -3,6 +3,6 @@
     users.users.akarl = {
         isNormalUser = true;
         shell = pkgs.zsh;
-        extraGroups = [ "wheel" "lp" "cups" ];
+        extraGroups = [ "wheel" "lp" "cups" "scanner" ];
     };
 }