message: add a note on numpy compatibility.
  refers to
diff: @@ -1433,6 +1433,16 @@ def reduce_mean(input_tensor,
  @compatibility(numpy)
  Equivalent to np.mean
  +
  + Please note that `np.mean` has a `dtype` parameter that could be used to specify the output type. By default this is `dtype=float64`. On the other hand, `tf.reduce_mean` has an aggressive type inference from `input_tensor`, for example:
  +
  + ```python
  + x = tf.constant([1, 0, 1, 0])
  + tf.reduce_mean(x) # 0
  + y = tf.constant([1., 0., 1., 0.])
  + tf.reduce_mean(y) # 0.5
  + ```
  +
  @end_compatibility
  """
  if keep_dims is not None:
  