Add instructions for pip install via easy_install.

Add a line item to easy_install pip since we now need to pip install
openstack.nose_plugin. Fixes bug 951019

Change-Id: Ibf4b8bb7feac2b8290db2f4c4665dacf8a881462

doc/source/development_saio.rst

@@ -32,6 +32,7 @@ Installing dependencies and the core code
      python-coverage python-dev python-nose python-setuptools python-simplejson
      python-xattr sqlite3 xfsprogs python-webob python-eventlet
      python-greenlet python-pastedeploy python-netifaces`
+  #. `easy_install pip`
   #. `pip install openstack.nose_plugin`
   #. Install anything else you want, like screen, ssh, vim, etc.