composite index creation is documented [here](https://cloud.google.com/datastore/docs/tools/indexconfig). It would be a good to add a reference to it in `Query.java` and [here](https://github.com/GoogleCloudPlatform/gcloud-java/tree/master/gcloud-java-datastore#running-a-query).
composite index creation is documented here.
It would be a good to add a reference to it in
Query.javaand here.