message: Add docstring for strings.reduce_join
  Fixes
diff: @@ -352,6 +352,31 @@ def reduce_join_v2( # pylint: disable=missing-docstring
  keepdims=False,
  separator="",
  name=None):
  + """Joins all strings into a single string, or joins along an axis.
  +
  + >>> tf.strings.reduce_join([['abc','123'],
  + ... ['def','456']]).numpy()
  + b'abc123def456'
  + >>> tf.strings.reduce_join([['abc','123'],
  + ... ['def','456']], axis=-1).numpy()
  + array([b'abc123', b'def456'], dtype=object)
  + >>> tf.strings.reduce_join([['abc','123'],
  + ... ['def','456']],
  + ... axis=-1,
  + ... separator=" ").numpy()
  + array([b'abc 123', b'def 456'], dtype=object)
  +
  + Args:
  + input: A `tf.string` tensor.
  + axis: Which axis to join along. The default behavior is to join all
  + elements, producing a scalar.
  + keepdims: If true, retains reduced dimensions with length 1.
  + separator: a string added between each string being joined.
  + name: A name for the operation (optional).
  +
  + Returns:
  + A `tf.string` tensor.
  + """
  with ops.name_scope(None, "ReduceJoin", [inputs, axis]):
  inputs_t = ops.convert_to_tensor(inputs)
  axis = _reduce_join_reduction_dims(inputs_t, axis)
  