message: Updates description & example usage
  Made changes per issue
  Updated description to mention tf.Keras model.
  Added the missing line in the example usage for SavedModel and tf.keras model.
diff: @@ -291,7 +291,7 @@ class TFLiteConverterV2(object):
  class TFLiteConverter(object):
  """Convert a TensorFlow model into `output_format` using TOCO.
  - This is used to convert from a TensorFlow GraphDef or SavedModel into either a
  + This is used to convert from a TensorFlow GraphDef, SavedModel or tf.keras model into either a
  TFLite FlatBuffer or graph visualization.
  Attributes:
  @@ -370,10 +370,12 @@ class TFLiteConverter(object):
  # Converting a SavedModel.
  converter = lite.TFLiteConverter.from_saved_model(saved_model_dir)
  tflite_model = converter.convert()
  + open("converted_model.tflite", "wb").write(tflite_model)
  # Converting a tf.keras model.
  converter = lite.TFLiteConverter.from_keras_model_file(keras_model)
  tflite_model = converter.convert()
  + open("converted_model.tflite", "wb").write(tflite_model)
  ```
  """
  