Add README in the devstack folder

This adds a README.rst in the devstack folder with information
about DevStack and how to install Patrole plugin in Devstack.

Change-Id: I31a92351211a2f37403c08406215bc10f3c3222e
diff --git a/doc/source/installation.rst b/doc/source/installation.rst
index b9cc924..827239f 100644
--- a/doc/source/installation.rst
+++ b/doc/source/installation.rst
@@ -26,10 +26,4 @@
 DevStack Installation
 =====================
 
-Patrole can be installed like any other DevStack plugin by including the
-``install_plugin`` directive inside local.conf::
-
-    [[local|localrc]]
-    ...
-
-    enable_plugin patrole git://git.openstack.org/openstack/patrole
+.. include:: ../../devstack/README.rst