Add example configuration for running our tests with nova

This is essentially taken from our devstack plugin, removing bits
required for standalone tests (to be covered later).

Change-Id: I2f213ded1298833f5b4c1b712112bc9f1856671e
diff --git a/doc/source/usage.rst b/doc/source/usage.rst
index 8ab88eb..3e3c56e 100644
--- a/doc/source/usage.rst
+++ b/doc/source/usage.rst
@@ -19,7 +19,14 @@
     [service_enabled]
     ironic_inspector = True
 
-.. TODO(dtantsur): I'm pretty sure more configuration is required, fill it in
+See the following example configurations for more details:
+
+.. toctree::
+   :maxdepth: 1
+
+   config/with-nova
+
+.. TODO(dtantsur): cover standalone tests
 
 .. _Tempest configuration: https://docs.openstack.org/tempest/latest/configuration.html