Add Apache License Content in index.rst

Add Apache License 2.0 Content which is necessary
for ./releasenotes/source/index.rst.

Change-Id: Ieda2bda1eadc26a1e3420aecd3bee1b64ae3e23f

releasenotes/source/index.rst

@@ -1,3 +1,17 @@
+..
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+=================================================
 Welcome to watcher's Release Notes documentation!
 =================================================