doc/libavcodec: hint to where to find the Git history

Signed-off-by: Alexander Strasser <eclipse7@gmx.net>

doc/libavcodec.texi

@@ -1120,7 +1120,7 @@ ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1)
 @c man end
 
 @c man begin AUTHORS
-See git history
+See Git history (git://source.ffmpeg.org/ffmpeg)
 @c man end
 
 @end ignore