Add file acknowledging the 3rdparty code we ship

Change-Id: I0a09eb7f11b92ca76698ad2b280854cb27de8127
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>
Reviewed-by: Niels Weber <niels.weber@digia.com>