Fixed broken link in readme.rst
The external example link to blockdiag.com was broken and so I updated it with the proper link.
@@ -19,7 +19,7 @@ Features
* Multilingualization for node-label (utf-8 only).
You can get some examples and generated images on
-`blockdiag.com <http://blockdiag.com/blockdiag/build/html/index.html>`_ .
+`blockdiag.com <http://blockdiag.com/en/blockdiag/examples.html>`_ .
Setup
=====
