message: [tf.data] Update `parallel_batch` optimization description.
diff: @@ -177,8 +177,13 @@ class OptimizationOptions(options.OptionsBase):
  parallel_batch = options.create_option(
  name="parallel_batch",
  ty=bool,
  - docstring="Whether to parallelize copying of batch elements. If None, "
  - "defaults to False.")
  + docstring="Whether to parallelize copying of batch elements. This "
  + "optimization is highly experimental and can cause performance "
  + "degradation (e.g. when the parallelization overhead exceeds the "
  + "benefits of performing the data copies in parallel). You should only "
  + "enable this optimization if a) your input pipeline is bottlenecked on "
  + "batching and b) you have validated that this optimization improves "
  + "performance. If None, defaults to False.")
  reorder_data_discarding_ops = options.create_option(
  name="reorder_data_discarding_ops",
  