[devel] Mention zlib-libpng license in each source file
diff --git a/scripts/makefile.darwin b/scripts/makefile.darwin
index bc39865..1bc3527 100644
--- a/scripts/makefile.darwin
+++ b/scripts/makefile.darwin
@@ -4,6 +4,8 @@
 # derived from makefile.linux:
 #  Copyright (C) 1998, 1999 Greg Roelofs
 #  Copyright (C) 1996, 1997 Andreas Dilger
+#
+# This code is released under the zlib-libpng license.
 # For conditions of distribution and use, see copyright notice in png.h
 
 # where "make install" puts libpng.a, libpng14.dylib, png.h and pngconf.h