Add a page for release 16 to release notes

Change-Id: I526c38204af390ea04e261fe075cb1aff987005c
diff --git a/releasenotes/source/index.rst b/releasenotes/source/index.rst
index cea76b4..adec7a7 100644
--- a/releasenotes/source/index.rst
+++ b/releasenotes/source/index.rst
@@ -6,6 +6,7 @@
     :maxdepth: 1
 
     unreleased
+    v16.0.0
     v15.0.0
     v14.0.0
     v13.0.0