add missing license header

Author: Mpdreamz

tests/authoring/Framework/TestCrossLinkResolver.fs

@@ -1,3 +1,7 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information
+
 namespace authoring
 
 open System