message: Improve nest.map_structure docstring
diff: @@ -740,19 +740,51 @@ def map_structure(func, *structure, **kwargs):
  Examples:
  - 1. A single Python dict:
  + * A single Python dict:
  >>> a = {"hello": 24, "world": 76}
  >>> tf.nest.map_structure(lambda p: p * 2, a)
  {'hello': 48, 'world': 152}
  - 2. Multiple Python dictionaries:
  + * Multiple Python dictionaries:
  >>> d1 = {"hello": 24, "world": 76}
  >>> d2 = {"hello": 36, "world": 14}
  >>> tf.nest.map_structure(lambda p1, p2: p1 + p2, d1, d2)
  {'hello': 60, 'world': 90}
  + * A single Python list:
  +
  + >>> a = [24, 76, "ab"]
  + >>> tf.nest.map_structure(lambda p: p * 2, a)
  + [48, 152, 'abab']
  +
  + * Scalars:
  +
  + >>> tf.nest.map_structure(lambda x, y: x + y, 3, 4)
  + 7
  +
  + * Empty structures:
  +
  + >>> tf.nest.map_structure(lambda x: x + 1, ())
  + ()
  +
  + *. Check the types of iterables:
  +
  + >>> s1 = (((1, 2), 3), 4, (5, 6))
  + >>> s1_list = [[[1, 2], 3], 4, [5, 6]]
  + >>> tf.nest.map_structure(lambda x, y: None, s1, s1_list)
  + Traceback (most recent call last):
  + ...
  + TypeError: The two structures don't have the same nested structure
  +
  + * Type check is set to False:
  +
  + >>> s1 = (((1, 2), 3), 4, (5, 6))
  + >>> s1_list = [[[1, 2], 3], 4, [5, 6]]
  + >>> tf.nest.map_structure(lambda x, y: None, s1, s1_list, check_types=False)
  + (((None, None), None), None, (None, None))
  +
  Args:
  func: A callable that accepts as many arguments as there are structures.
  *structure: scalar, or tuple or dict or list of constructed scalars and/or
  