Add releasenote page for v39.0.0

Change-Id: Ifa42169ef047a73b31dc389687b41a6472b49fa5
diff --git a/releasenotes/source/index.rst b/releasenotes/source/index.rst
index e3018b4..f36c837 100644
--- a/releasenotes/source/index.rst
+++ b/releasenotes/source/index.rst
@@ -6,6 +6,7 @@
    :maxdepth: 1
 
    unreleased
+   v39.0.0
    v38.0.0
    v37.0.0
    v36.0.0