Update README

Author: tpeczek

README.md

@@ -5,6 +5,7 @@ Sample project for demonstrating Push Notifications based on Push API and Web Pu
 - [Push API](https://www.tpeczek.com/2017/12/push-notifications-and-aspnet-core-part.html)
 - [Requesting Delivery](https://www.tpeczek.com/2018/01/push-notifications-and-aspnet-core-part.html) ([Lib.Net.Http.WebPush](https://github.com/tpeczek/Lib.Net.Http.WebPush))
 - VAPID tokens caching
+- [Replacing Messages & Urgency](https://www.tpeczek.com/2018/01/push-notifications-and-aspnet-core-part_18.html)
 
 ## Donating