Update to document the :title feature on show page

Author: amalagaura

docs/6-show-screens.md

@@ -34,3 +34,10 @@ If you'd like to keep the default active_admin look, you can also use "attribute
         active_admin_comments
       end
     end
+
+You can customize the title of the object in the show screen.  The default is the resouce name and the ID.  You can customize as follows:
+    
+    show :title => :name do
+    end
+
+