Update master for stable/stein

Add file to the reno documentation build to show release notes for
stable/stein.

Use pbr instruction to increment the minor version number
automatically so that master versions are higher than the versions on
stable/stein.

Change-Id: I1b79f8a70ae21003eb9aaf3dea618356c11c2d25
Sem-Ver: feature
diff --git a/releasenotes/source/index.rst b/releasenotes/source/index.rst
index ca4384e..38ba3eb 100644
--- a/releasenotes/source/index.rst
+++ b/releasenotes/source/index.rst
@@ -6,6 +6,7 @@
    :maxdepth: 1
 
    unreleased
+   stein
    v0.5.0
    v0.4.0
    v0.3.0