Added a note about installing python-dev in README.

Author: stephenmcd

README.rst

@@ -22,9 +22,11 @@ Installation
 ============
 
 Note that if you've never installed gevent, you'll first need to
-install the libevent development library. This can be achieved on
-Debian based sytems with the following command::
+install the libevent development library. You may also need the Python
+development library if not installed. This can be achieved on Debian
+based sytems with the following command::
 
+    $ sudo apt-get install python-dev
     $ sudo apt-get install libevent-dev
 
 The easiest way to install django-socketio is directly from PyPi using