Add paragraph about PDF code of conduct.

Author: mdboom

doc/_templates/index.html

@@ -141,6 +141,10 @@ <h4>Other learning resources</h4>
 
   <h4>Need help?</h4>
 
+<p>matplotlib is a welcoming, inclusive project, and we try to follow
+the <a href="http://www.python.org/psf/codeofconduct/">Python Software
+Foundation Code of Conduct</a> in everything we do.</p>
+
 <p>Check the <a href="{{ pathto('faq/index') }}">faq</a>,
 the <a href="{{ pathto('api/index') }}">api</a> docs,
 <a href="http://matplotlib.1069221.n5.nabble.com/matplotlib-users-f3.html">mailing