clients/simple-dmabuf-v4l: Dmabuf-contiguous for vivid module

For certain cases when using vivid module, some display-controllers
require to allocate the dmabuf in a contiguous fashion so explain that
to the user when adding details about vivid module.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

clients/simple-dmabuf-v4l.c

@@ -960,6 +960,9 @@ usage(const char *argv0)
 	       "  here we assume /dev/video0\n"
 	       "- set the pixel format:\n"
 	       "    $ v4l2-ctl -d /dev/video0 --set-fmt-video=width=640,pixelformat=XR24\n"
+	       "- optionally could add 'allocators=0x1' to options as to create"
+	       "  the buffer in a dmabuf-contiguous way\n"
+	       "  (as some display-controllers require it)\n"
 	       "- launch the demo:\n"
 	       "    $ %s -v /dev/video0 -f XR24 -d XR24\n"
 	       "You should see a test pattern with color bars, and some text.\n"