[docs] Fixed wrong openwrt.org link in README

Author: nemesifier

README.rst

@@ -19,7 +19,7 @@ netjsonconfig
 
 ------------
 
-Netjsonconfig is part of the `OpenWISP project <http://openwrt.org>`_ and it's the official
+Netjsonconfig is part of the `OpenWISP project <http://openwisp.org>`_ and it's the official
 configuration engine of `OpenWISP 2 <https://github.com/openwisp/ansible-openwisp2>`_.
 
 .. image:: http://netjsonconfig.openwisp.org/en/latest/_images/openwisp.org.svg