message: Minor clarification to model_to_estimator() doc string
diff: @@ -458,10 +458,14 @@ def model_to_estimator(keras_model=None,
  @{$programmers_guide/estimators$creating_estimators_from_keras_models}.
  Args:
  - keras_model: Keras model in memory.
  - keras_model_path: Directory to a keras model on disk.
  + keras_model: A compiled Keras model object. This argument is mutually
  + exclusive with `keras_model_path`.
  + keras_model_path: Path to a compiled Keras model saved on disk, in HDF5
  + format, which can be generated with the `save()` method of a Keras model.
  + This argument is mutually exclusive with `keras_model`.
  custom_objects: Dictionary for custom objects.
  - model_dir: Directory to save Estimator model parameters, graph and etc.
  + model_dir: Directory to save Estimator model parameters, graph, summary
  + files for TensorBoard, etc.
  config: Configuration object.
  Returns:
  @@ -473,7 +477,7 @@ def model_to_estimator(keras_model=None,
  ValueError: if the keras_model_path is a GCS URI.
  ValueError: if keras_model has not been compiled.
  """
  - if (not keras_model) and (not keras_model_path):
  + if not (keras_model or keras_model_path):
  raise ValueError(
  'Either `keras_model` or `keras_model_path` needs to be provided.')
  if keras_model and keras_model_path:
  @@ -495,8 +499,9 @@ def model_to_estimator(keras_model=None,
  if not hasattr(keras_model, 'optimizer') or not keras_model.optimizer:
  raise ValueError(
  - 'The given keras model has not been compiled yet. Please compile first '
  - 'before calling `model_to_estimator`.')
  + 'The given keras model has not been compiled yet. '
  + 'Please compile the model with `model.compile()` '
  + 'before calling `model_to_estimator()`.')
  if isinstance(config, dict):
  config = run_config_lib.RunConfig(**config)
  