message: [tf.data] Update `map` documentation -- calling out the fact that setting `num_parallel_calls` results in asynchronous computation.
diff: @@ -970,8 +970,8 @@ class DatasetV2(object):
  shapes and types defined by `self.output_shapes` and
  `self.output_types`) to another nested structure of tensors.
  num_parallel_calls: (Optional.) A `tf.int32` scalar `tf.Tensor`,
  - representing the number elements to process in parallel. If not
  - specified, elements will be processed sequentially. If the value
  + representing the number elements to process asynchronously in parallel.
  + If not specified, elements will be processed sequentially. If the value
  `tf.data.experimental.AUTOTUNE` is used, then the number of parallel
  calls is set dynamically based on available CPU.
  