clarify batching in docs

Author: Ajay Kannan

gcloud-java-datastore/src/main/java/com/google/gcloud/datastore/QueryResults.java

@@ -22,7 +22,8 @@
  * The result of a Google Cloud Datastore query submission.
  * When the result is not typed it is possible to cast it to its appropriate type according to
  * the {@link #resultClass} value.
- * Results are loaded lazily; therefore it is possible to get a {@code DatastoreException}
+ * Results are loaded lazily in batches, where batch size is set by Cloud Datastore. As a result, it
+ * is possible to get a {@code DatastoreException}.
  * upon {@link Iterator#hasNext hasNext} or {@link Iterator#next next} calls.
  *
  * @param <V> the type of the results value.