LURE: Add a comment explaining why kADFlagUseExtraAsHint is used

For the records, this was introduced by Eugene in SVN revision 30106,
corresponding to git commit b87b0f21

engines/lure/detection.cpp

@@ -180,6 +180,9 @@ public:
 	LureMetaEngine() : AdvancedMetaEngine(Lure::gameDescriptions, sizeof(Lure::LureGameDescription), lureGames) {
 		_md5Bytes = 1024;
 		_singleid = "lure";
+
+		// Use kADFlagUseExtraAsHint to distinguish between EGA and VGA versions
+		// of italian Lure when their datafiles sit in the same directory.
 		_flags = kADFlagUseExtraAsHint;
 		_guioptions = Common::GUIO_NOSPEECH;
 	}