message: Improve explanation of shard
diff: @@ -973,7 +973,8 @@ class DatasetV2(tracking_base.Trackable, composite_tensor.CompositeTensor):
  def shard(self, num_shards, index):
  """Creates a `Dataset` that includes only 1/`num_shards` of this dataset.
  - For example:
  + `shard` is a deterministic operator; the Dataset produced by
  + `A.shard(n, i)` will contain all elements of A whose index mod n = i.
  ```python
  # Create a Dataset with 60 elements.
  @@ -987,9 +988,6 @@ class DatasetV2(tracking_base.Trackable, composite_tensor.CompositeTensor):
  # There is no overlap between Datasets B, C and D.
  ```
  - `shard` is a deterministic operator; the returned Dataset depends only
  - on the target Dataset, and the values of `num_shards` and `index`.
  -
  This dataset operator is very useful when running distributed training, as
  it allows each worker to read a unique subset.
  