Add a page for release 16.1 to release notes

Change-Id: Id148a6cc78c99218a6bca31fa6739cb84d1b49e2
diff --git a/releasenotes/source/index.rst b/releasenotes/source/index.rst
index d2be814..db01da0 100644
--- a/releasenotes/source/index.rst
+++ b/releasenotes/source/index.rst
@@ -6,6 +6,7 @@
     :maxdepth: 1
 
     unreleased
+    v16.1.0
     v16.0.0
     v15.0.0
     v14.0.0