#16 - Add link to Part 4 Swagger tutorial in readme

Author: AdamZink

README.md

@@ -13,3 +13,4 @@ Tutorials are available to explain the steps on [Medium](https://medium.com/@ada
 * [Part 1 - Create a Spring Boot application with Spring Initializr](https://medium.com/@adamzink/creating-an-api-with-spring-boot-and-mysql-part-1-4c5544a2a202)
 * [Part 2 - Create the first API endpoint to POST a User](https://medium.com/@adamzink/creating-an-api-with-spring-boot-and-mysql-part-2-1b3f5740c7bf)
 * [Part 3 - Create more API endpoints to GET, PUT, and DELETE Users](https://medium.com/@adamzink/creating-an-api-with-spring-boot-and-mysql-part-3-f1b5ef9334c0)
+* [Part 4 - Add API documentation with Swagger](https://medium.com/@adamzink/creating-an-api-with-spring-boot-and-mysql-part-4-d39edbe87b53)