Add state machine to documentation

Since we can now generate the state machine that ironic
uses using the tools/states_to_dot.py generator we can
now build it and include it in the documentation for others
to view.

Change-Id: I4ffc298d0708cbac2573e1e2aee2d73836c27a80

doc/source/dev/states.rst

@@ -0,0 +1,21 @@
+.. _states:
+
+======================
+Ironic's State Machine
+======================
+
+The diagram below shows the states that an Ironic node goes through during the
+lifetime of a node. The diagram also depicts the events that transition
+the node to different states.
+
+.. figure:: ../images/states.png
+   :width: 660px
+   :align: left
+   :alt: Ironic state transitions
+
+.. note::
+
+    For more information about the states, see the specification located at
+    `ironic-state-machine`_.
+
+.. _ironic-state-machine: http://specs.openstack.org/openstack/ironic-specs/specs/kilo/new-ironic-state-machine.html

doc/source/index.rst

@@ -30,6 +30,7 @@ Introduction
   :maxdepth: 1
 
   dev/architecture
+  dev/states
   dev/contributing
 
 .. toctree::