QT_QPA_EGLFS_ALWAYS_SET_MODE=1 needs to be exported, otherwise the Qt5
Cinematic demo throws a storm of the following messages:
Could not queue DRM page flip on screen LVDS1 (Invalid argument)
Improve the instructions by mentioning such requirement.
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>