Render devstack ansible roles via zuul-sphinx

Change-Id: Ie0db5bcfdacc2543488704fe4428b68910bd6bf1
diff --git a/doc/requirements.txt b/doc/requirements.txt
index e140bc0..f65e9df 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -8,3 +8,4 @@
 blockdiag
 sphinxcontrib-blockdiag
 sphinxcontrib-nwdiag
+zuul-sphinx>=0.2.0