This fix uses the \ingroup command to add the stereoscopic example to the
examples-widgets-opengl group.
I also elaborated on the hardware requirements.
Fixes: QTBUG-119280
Pick-to: 6.5 6.6
Change-Id: I6d5b992e533b897d84100f0f897aae97ef89290f
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>