Create service definition for nova-serialproxy

Nova has the ability to do remote interactive consoles but there is no
easy way to enable this in devstack.  This change defines a service
called n-serial to enable the service.  Documentation is added to a
new guide on nova, describing how to set further options in local.conf

Change-Id: I401d94b2413c62bfae9b90d2214d77bd4cfc15d5
diff --git a/doc/source/index.rst b/doc/source/index.rst
index 855a2d6..10f4355 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -67,6 +67,7 @@
    guides/multinode-lab
    guides/neutron
    guides/devstack-with-nested-kvm
+   guides/nova
 
 All-In-One Single VM
 --------------------
@@ -102,6 +103,11 @@
 <guides/devstack-with-nested-kvm>`. With this setup, Nova instances
 will be more performant than with plain QEMU emulation.
 
+Nova and devstack
+--------------------------------
+
+Guide to working with nova features :doc:`Nova and devstack <guides/nova>`.
+
 DevStack Documentation
 ======================