cookbook: Added comments to script example

Commented the ClutterScript example so it can be used
inline as part of the recipe, rather than as an
example in the appendix (it's too simple to warrant
a separate appendix).

doc/cookbook/examples/script-ui.c

@@ -11,6 +11,7 @@ main (int argc, char *argv[])
   gchar *filename = "script-ui.json";
   GError *error = NULL;
 
+  /* load a JSON file into the script */
   clutter_script_load_from_file (ui, filename, &error);
 
   if (error != NULL)
@@ -20,6 +21,7 @@ main (int argc, char *argv[])
       exit (EXIT_FAILURE);
     }
 
+  /* retrieve objects from the script */
   ClutterActor *stage;
 
   clutter_script_get_objects (ui,