Update README.md

Author: rcalago

kotlin-ktor/README.md

@@ -6,3 +6,4 @@ This module contains articles about Kotlin Libraries.
 - [An Introduction to Running GraphQL in Kotlin and Ktor](https://www.baeldung.com/kotlin/graphql-ktor)
 - [Creating a Web Application With Ktor and Thymeleaf](https://www.baeldung.com/kotlin/ktor-thymeleaf-web-application)
 - [A Look at the Ktor Client](https://www.baeldung.com/kotlin/ktor-client)
+- [Testing Ktor Controllers](https://www.baeldung.com/kotlin/ktor-test-controllers)