PPD: Document Default

ppd/PPD.pm

@@ -31,7 +31,8 @@ our @EXPORT = qw(define_group define_ui_group switch_group declare get set maybe
 #		  PS => string,		# PS code to emit (mandatory)
 #		  Default => 1,		# if this is the default value
 #		},
-#	]
+#	],
+#	Default => key,		# default value if not marked inside Values
 # }
 my %keywords = ();