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

Change-Id: If5c78f555fb737a18a3ae4c216ea3e2630b101bc
diff --git a/requirements.txt b/requirements.txt
index c3ae0c0..ab1a4f4 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: 2021 Open Networking Foundation <info@opennetworking.org>
+# SPDX-License-Identifier: Apache-2.0
+
 Sphinx~=4.1.2
 doc8~=0.9.0
 reuse~=0.13.0