Add testing goat book (#5416)

Co-authored-by: NKatarina <nymphadora96@gmail.com>

books/free-programming-books.md

@@ -2558,6 +2558,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [Djen of Django](http://agiliq.com/books/djenofdjango/)
 * [Effective Django](https://web.archive.org/web/20181130092020/http://www.effectivedjango.com/) (1.5)
 * [How to Tango With Django](http://www.tangowithdjango.com/book17/) (1.7)
+* [Test-Driven Development With Python And Django](http://www.obeythetestinggoat.com/pages/book.html) (1.11)
 
 
 #### Flask