fix layout example

fixes sqlpage#374

Thanks to @amrutadotorg for reporting the issue

examples/official-site/examples/layouts.sql

@@ -1,11 +1,15 @@
-select 'dynamic' as component, properties FROM example WHERE component = 'shell' LIMIT 1;
+select 'dynamic' as component, 
+    json_patch(properties->0, json_object('layout', coalesce($layout, 'boxed'))) as properties
+FROM example WHERE component = 'shell' LIMIT 1;
 
 select 'text' as component, '
 # Layouts
 
 SQLPage comes with a few built-in layouts that you can use to organize the general structure of your application.
 
 Click on one of the layouts below to try it out.
+
+For more information on how to use layouts, see the [shell component documentation](/documentation.sql?component=shell#component).
 ' as contents_md;
 
 select 'list' as component, 'Available SQLPage shell layouts' as title;