Explaining Gstreamer plugin example

[Wonchul Lee]

Hi Ivo,
There was a race condition in the wayland when multi-threaded clients
share wl_display/wl_surface. It could cause to set to the wrong
wayland queue.
The purpose of that example is to check that it fixes with this
change, https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/merge_requests/74

I think if you're using GStreamer 1.16 or later, you will not have the
same issue and don't need to do this way, so could you check the
version you are using?

Thanks,
Wonchul.