message: Improve tf.TensorShape.merge_with documentation
diff: @@ -925,8 +925,28 @@ class TensorShape(object):
  def merge_with(self, other):
  """Returns a `TensorShape` combining the information in `self` and `other`.
  - The dimensions in `self` and `other` are merged elementwise,
  - according to the rules defined for `Dimension.merge_with()`.
  + The dimensions in `self` and `other` are merged element-wise,
  + according to the rules below:
  +
  + ```python
  + Dimension(n).merge_with(Dimension(None)) == Dimension(n)
  + Dimension(None).merge_with(Dimension(n)) == Dimension(n)
  + Dimension(None).merge_with(Dimension(None)) == Dimension(None)
  + # raises ValueError for n != m
  + Dimension(n).merge_with(Dimension(m))
  + ```
  + >> ts = tf.TensorShape([1,2])
  + >> ot1 = tf.TensorShape([1,2])
  + >> ts.merge_with(ot).as_list()
  + [1,2]
  +
  + >> ot2 = tf.TensorShape([1,None])
  + >> ts.merge_with(ot2).as_list()
  + [1,2]
  +
  + >> ot3 = tf.TensorShape([None, None])
  + >> ot3.merge_with(ot2).as_list()
  + [1, None]
  Args:
  other: Another `TensorShape`.
  