Add part 3 to README.md

README.md

@@ -11,6 +11,7 @@ This repository contains a sample Java REST application implemented according to
 It is part of the HappyCoders tutorial series on Hexagonal Architecture:
 * [Part 1: Hexagonal Architecture - What Is It? Why Should You Use It?](https://www.happycoders.eu/software-craftsmanship/hexagonal-architecture/).
 * [Part 2: Hexagonal Architecture with Java - Tutorial](https://www.happycoders.eu/software-craftsmanship/hexagonal-architecture-java/).
+* [Part 3: Ports and Adapters Java Tutorial: Adding a Database Adapter](https://www.happycoders.eu/software-craftsmanship/ports-and-adapters-java-tutorial-db/).
 
 In the main branch, you'll find the application implemented without an application framework. It's only using:
 * [RESTEasy](https://resteasy.dev/) (implementing [Jakarta RESTful Web Services](https://jakarta.ee/specifications/restful-ws/)),