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/devstack/README.rst b/devstack/README.rst
new file mode 100644
index 0000000..053afd4
--- /dev/null
+++ b/devstack/README.rst
@@ -0,0 +1,25 @@
+====================
+Enabling in Devstack
+====================
+
+.. warning::
+
+  The ``stack.sh`` script must be run in a disposable VM that is not
+  being created automatically. See the `README file`_ in the DevStack
+  repository for more information.
+
+1. Download DevStack::
+
+     git clone https://git.openstack.org/openstack-dev/devstack.git
+     cd devstack
+
+2. Patrole can be installed like any other DevStack plugin by including the
+   ``enable_plugin`` directive inside local.conf::
+
+     > cat local.conf
+     [[local|localrc]]
+     enable_plugin patrole https://git.openstack.org/openstack/patrole
+
+3. Run ``stack.sh`` found in the DevStack repo.
+
+.. _README file: https://github.com/openstack-dev/devstack/blob/master/README.rst