Documentation for single interface Neutron networking with OVS

Change-Id: I7a72377f55952db629c2ce7ba4ed648635e581ef
diff --git a/tox.ini b/tox.ini
index 279dcd4..f76e256 100644
--- a/tox.ini
+++ b/tox.ini
@@ -32,6 +32,10 @@
    sphinx>=1.1.2,<1.2
    pbr>=0.6,!=0.7,<1.0
    oslosphinx
+   nwdiag
+   blockdiag
+   sphinxcontrib-blockdiag
+   sphinxcontrib-nwdiag
 whitelist_externals = bash
 setenv =
   TOP_DIR={toxinidir}