message: Update API docs for SamplingDataset op
  Update API doc for SamplingDataset
  Fix string quoting
  Add description field
diff: @@ -4,8 +4,8 @@ op {
  in_arg {
  name: "rate"
  description: <<END
  -A scalar representing the sample rate of elements from the `input_dataset`
  -that should be taken.
  +A scalar representing the sample rate. Each element of `input_dataset` is
  +retained with this probability, independent of all other elements.
  END
  }
  in_arg {
  @@ -20,5 +20,10 @@ END
  A scalar representing seed2 of random number generator.
  END
  }
  - summary: "Creates a dataset that contains `rate` elements from the `input_dataset`."
  + summary: "Creates a dataset that takes a Bernoulli sample of the contents of another dataset."
  + description: <<END
  +There is no direct Python API for creating Datasets of this type. Rewrite rules in
  +`tensorflow/core/grappler/optimizers/data/filter_with_random_uniform_fusion.cc`
  +create instances of this dataset.
  +END
  }
  