Use service_available

To enable tests in tempest the services need to be added
to `service_available` and not `service_enabled`

Change-Id: Id4fd48d98f521f8ab3c49ccb12f8c770bc787c21
diff --git a/doc/source/usage.rst b/doc/source/usage.rst
index 27b5ebe..ecb7218 100644
--- a/doc/source/usage.rst
+++ b/doc/source/usage.rst
@@ -9,14 +9,14 @@
 
 .. code-block:: ini
 
-    [service_enabled]
+    [service_available]
     ironic = True
 
 If introspection tests are needed, also enable support for ironic-inspector:
 
 .. code-block:: ini
 
-    [service_enabled]
+    [service_available]
     ironic_inspector = True
 
 See the following example configurations for more details: