Update 'README.md'

README.md

@@ -6,4 +6,10 @@
   final FlutterTts flutterTts = FlutterTts();
 
     await flutterTts.setSharedInstance(true);
-```
+```
+
+
+## Reference
+
+- [flutter_tts](https://pub.dev/packages/flutter_tts)
+-