add the content in README.rst file

Change-Id: I09b84df0073f2bab30d03886a1b4f4b9fcf15527

README.rst

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+============
+Nova Formula
+============
+
+Install and configure the OpenStack Nova service.
+
+.. note::
+    See the full `Salt Formulas installation and usage instructions
+    <http://docs.saltstack.com/en/latest/topics/development/conventions/formulas.html>`_.
+
+Available states
+================
+
+.. contents::
+    :local:
+
+``nova.db``
+-----------
+
+Create the db for Nova service.
+
+``nova.keystone``
+-----------------
+
+Init the Nova user, service and endpoint.
+
+``nova.all-in-one``
+-------------------
+
+Install the Nova service all in one mode.
+
+``nova.controller``
+-------------------
+
+Install the Nova service on controller node.
+
+``nova.compute``
+----------------
+
+Install the Nova service on compute node.