Documentation file for explaning in more detail how to run weston, using
launcher direct and specifying a non-default seat. This explains how to
create a udev file and assign a particular GPU card to it, and
potentially, other input devices. It also describes a bit additional
arguments that can be passed on, as an introduction to using the DRM
node for that particular seat.
Fixes#460
Signed-off-by: Marius Vlad <marius.vlad@collabora.com>