message: Improve error message for shard_dataset_op to mention AutoShardPolicy.
diff: @@ -145,12 +145,13 @@ class ShardDatasetOp::Dataset : public DatasetBase {
  Status s = input_impl_->GetNext(ctx, &unused_result, end_of_sequence);
  if (*end_of_sequence || errors::IsOutOfRange(s)) {
  return errors::InvalidArgument(
  - "There aren't enough elements in this dataset for each shard "
  - "to have at least one element (# elems = ",
  + "There aren't enough elements in this dataset for each shard to "
  + "have at least one element (# elems = ",
  next_index_, ", ", "# shards = ", dataset()->num_shards_,
  - "). If you are using ",
  - "datasets with distribution strategy, consider turning ",
  - "dataset autosharding off with `tf.data.Options`.");
  + "). If you are using datasets with distribution strategy, "
  + "considering setting the auto sharding policy to either DATA or "
  + "OFF using the `experimental_distribute.auto_shard_policy` option"
  + "of `tf.data.Options()`.");
  } else if (!s.ok()) {
  return s;
  }
  