Add setuptools to the dependencies in install.rst

We were using it already, better to admit the dependency.

Author: andreabedini

doc/source/install.rst

@@ -212,6 +212,7 @@ installed), make sure you have `nose
 Dependencies
 ------------
 
+* `setuptools <http://pythonhosted.org/setuptools>`__
 * `NumPy <http://www.numpy.org>`__: 1.7.0 or higher
 * `python-dateutil <http://labix.org/python-dateutil>`__ 1.5 or higher
 * `pytz <http://pytz.sourceforge.net/>`__