message: Clarify autoshard policy AUTO warning when input data is not file-based.
diff: @@ -653,9 +653,9 @@ Status OptimizeGraph(const GrapplerItem& item, int64 num_workers, int64 index,
  default:
  Status s = ShardByFile(*sink_node, num_workers, index, &flib, &graph);
  if (errors::IsNotFound(s)) {
  - LOG(WARNING) << "In AUTO-mode, and switching to DATA-based sharding, "
  - "instead of FILE-based sharding as we cannot find "
  - "appropriate reader dataset op(s) to shard. Error: "
  + LOG(WARNING) << "AUTO sharding policy will apply DATA sharding policy "
  + "as it failed to apply FILE sharding policy because of "
  + "the following reason: "
  << s.error_message();
  return ShardByData(*sink_node, num_workers, index, num_replicas,
  &graph);
  