firestore: document operators
@@ -169,6 +169,8 @@ build up a query using Select, Where and other methods of Query.
q := states.Where("pop", ">", 10).OrderBy("pop", firestore.Desc)
+Supported operators include `<`, `<=`, `>`, `>=`, and `==`.
+
Call the Query's Documents method to get an iterator, and use it like
the other Google Cloud Client iterators.
