Create releasenotes page for tempest 37.0.0, 38.0.0

Depends-On: https://review.opendev.org/c/openstack/releases/+/913952
Change-Id: I0840bbeafb3a2398998ccf199cab04067cb74b0c
diff --git a/releasenotes/source/index.rst b/releasenotes/source/index.rst
index 989d3b5..e3018b4 100644
--- a/releasenotes/source/index.rst
+++ b/releasenotes/source/index.rst
@@ -6,6 +6,8 @@
    :maxdepth: 1
 
    unreleased
+   v38.0.0
+   v37.0.0
    v36.0.0
    v35.0.0
    v34.2.0