install webcam_overlay_mix_audio.sh script

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
Add GLC_PIPE_DELAY param

http://ffmpeg.org/pipermail/ffmpeg-devel/2014-March/155704.html

A webcam video initialization can take ~280-300ms. This may induce
synch issue between audio video. It is possible to configure a delay
between the time where the pipe reader process is created and the time
where the first frame is written to the pipe to address this issue.

Signed-off-by: Olivier Langlois <olivier@trillion01.com>