added installation to the index

Resources/doc/index.rst

@@ -33,6 +33,7 @@ Tutorial
    :maxdepth: 1
    :numbered:
 
+   tutorial/creating_your_first_admin_class/installation
    tutorial/creating_your_first_admin_class/introduction
    tutorial/creating_your_first_admin_class/defining_entities
    tutorial/creating_your_first_admin_class/defining_routing