Added Tox to dev requirements
diff --git a/doc/installation.rst b/doc/installation.rst
index 89d0979..a9f779c 100644
--- a/doc/installation.rst
+++ b/doc/installation.rst
@@ -47,6 +47,7 @@
     - nose
     - sphinx
     - pyasn1
+    - tox
 
 Once these are installed, use Mercurial_ to get a copy of the source::