Change license from ONF-Member-Only to Apache-2.0

Change-Id: If5c78f555fb737a18a3ae4c216ea3e2630b101bc
diff --git a/Makefile b/Makefile
index 2b41867..0cdbd72 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: 2021 Open Networking Foundation <info@opennetworking.org>
+# SPDX-License-Identifier: Apache-2.0
+
 # Makefile for Sphinx documentation
 
 # use bash for pushd/popd, and to fail quickly