Add effective django

free-programming-books.md

@@ -1221,6 +1221,7 @@ See also [TeX](#tex)
 * [Djen of Django](http://agiliq.com/books/djenofdjango/)
 * [Django by Example](http://www.lightbird.net/dbe/)
 * [Django by Example for Django 1.5](http://lightbird.net/dbe2/)
+* [Effective Django](http://effectivedjango.com/)
 * [Tango With Django](http://www.tangowithdjango.com/book/)
 * [Deploy Django](http://www.deploydjango.com)