message: Add an explicit reason for NotImplementedError on eager model save
diff: @@ -1355,7 +1355,9 @@ class Network(base_layer.Layer):
  ```
  """
  if not self._is_graph_network:
  - raise NotImplementedError
  + raise NotImplementedError(
  + 'Currently `save` requires model to be a graph network. Consider '
  + 'using `save_weights`, in order to save the weights of the model.')
  from tensorflow.python.keras.models import save_model # pylint: disable=g-import-not-at-top
  save_model(self, filepath, overwrite, include_optimizer)
  