fix dead link of nice example

README.md

@@ -15,4 +15,4 @@ python-nbxmpp is a Python library that provides a way for Python applications to
 
  * [Downloads](http://dev.gajim.org/gajim/python-nbxmpp/tags)
  * You can also clone the git repository at http://dev.gajim.org/gajim/python-nbxmpp.git
- * [Example](http://dev.gajim.org/gajim/python-nbxmpp/tree/master/doc/examples)
\ No newline at end of file
+ * [Example](https://dev.gajim.org/gajim/python-nbxmpp/blob/master/doc/examples/xsend.py)
\ No newline at end of file