nixos/lorri: add to environment.systemPackages

most likely, people enabling the lorri module also want to use it,
without explicitly having to add it to users.users.<username>.packages.

cc @curiousleo @Profpatsch

nixos/modules/services/development/lorri.nix

@@ -41,5 +41,7 @@ in {
         Restart = "on-failure";
       };
     };
+
+    environment.systemPackages = [ pkgs.lorri ];
   };
 }