Add v13.0.0 release note page

Now that tempest 13.0.0 has been pushed [1] for the newton release lets
create a distinct releasenotes page for it.

[1] https://pypi.python.org/pypi/Tempest/13.0.0

Change-Id: I75e822f2ad354e1276e5a523b794b60942069b0c
diff --git a/releasenotes/source/v13.0.0.rst b/releasenotes/source/v13.0.0.rst
new file mode 100644
index 0000000..39816e4
--- /dev/null
+++ b/releasenotes/source/v13.0.0.rst
@@ -0,0 +1,6 @@
+=====================
+v13.0.0 Release Notes
+=====================
+
+.. release-notes:: 13.0.0 Release Notes
+   :version: 13.0.0