To match the updated example. Display a screenshot for both
Android and OS X in the gallery example documentation.

Change-Id: I37e56437bb54248a4d500810c56ce8a8ba15b4d2
Reviewed-by: J-P Nurmi <jpnurmi@theqtcompany.com>
Reviewed-by: Venugopal Shivashankar <venugopal.shivashankar@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>