docs: def track_model(model):
      '''
      Perform designated transformations on model, when it saves.
  
      Calls :py:func:`~simpleimages.utils.perform_transformation`
      on every model saves using
      :py:data:`django.db.models.signals.post_save`.
  
      It uses the ``update_fields`` kwarg to tell what fields it should
      transform.
      '''
      @receiver(post_save, sender=model, weak=False, dispatch_uid='simpleimages')
      def transform_signal(sender, **kwargs):
          simpleimages.utils.perform_transformation(
              kwargs['instance'],
              kwargs['update_fields']
          )
  
      def disconnect():
          post_save.disconnect(sender=model, dispatch_uid='simpleimages')
      return disconnect