Doc: Copy minimal example code into overview page

After change cfe53bce

, the 'minimal' example isn't that minimal anymore.
Rather copy the few lines, like we already do for the widget example.

Change-Id: I9dd818738edb8d229f54ff24822d4c1723376ccc
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>