README.rst: Replace a reference to ryu-plugin with ofagent

Ryu-plugin is obsolete and has been removed in the development version
of OpenStack/Networking.

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

README.rst

@@ -24,10 +24,7 @@ If you prefer to install Ryu from the source code::
    % cd ryu; python ./setup.py install
 
 If you want to use Ryu with `OpenStack <http://openstack.org/>`_,
-please refer `detailed documents <http://ryu.readthedocs.org/en/latest/using_with_openstack.html>`_.
-You can create tens of thousands of isolated virtual networks without
-using VLAN.  The Ryu application is included in OpenStack mainline as
-of Essex release.
+please refer `networking-ofagent project <https://github.com/stackforge/networking-ofagent>`_.
 
 If you want to write your Ryu application, have a look at
 `Writing ryu application <http://ryu.readthedocs.org/en/latest/writing_ryu_app.html>`_ document.