docs(keyboard): add an online web tool that can generate keymaps intuitively

modules/system/keyboard.nix

@@ -45,6 +45,7 @@ in
       description = lib.mdDoc ''
         List of keyboard mappings to apply, for more information see
         <https://developer.apple.com/library/content/technotes/tn2450/_index.html>.
+        <https://hidutil-generator.netlify.app/>.
       '';
     };
   };