Tweaked unittests for Python 3.x
diff --git a/doc/installation.rst b/doc/installation.rst
index a9f779c..0880d6f 100644
--- a/doc/installation.rst
+++ b/doc/installation.rst
@@ -48,6 +48,7 @@
     - sphinx
     - pyasn1
     - tox
+    - unittest2 (Python 2.x) or unittest2py3k (Python 3.x)
 
 Once these are installed, use Mercurial_ to get a copy of the source::