added comments from other '.pl' files

build/mac/TinderboxMozilla.pl

@@ -22,6 +22,8 @@
 
 $DEBUG = 1;
 
+	# One of them should be 1. This will come from a config file at some stage.
+	# In the meanwhile, it should match mozilla/config/mac/MacConfig.h
 $MOZ_LITE   = 0;
 $MOZ_MEDIUM = 1;
 $MOZ_DARK   = 0;