add license for sound

license.txt

@@ -26,6 +26,7 @@ CC BY-SA 3.0 UNPORTED. Created by D00Med
 
 Roar.ogg - CC BY 3.0 Mike Koenig - http://soundbible.com/1165-Dinosaur-Roar.html
 Velociraptor.ogg - CC BY 3.0 snottyboi - http://soundbible.com/1373-Velociraptor-Call.html
+dmobs_chirrup.ogg - CC BY SA 3.0 taikedz
 
 --License of lib_mount:
 -- Minetest mod: lib_mount
@@ -45,4 +46,5 @@ Velociraptor.ogg - CC BY 3.0 snottyboi - http://soundbible.com/1373-Velociraptor
 
 -- License of source code:
 -- -----------------------
--- WTFPL
\ No newline at end of file
+-- WTFPL
+