Add external example (Kotlin#20)

Add link to external example

Author: lorenzsimon

ReadMe.md

@@ -27,7 +27,7 @@ when needed
 
 ## External examples
 
-// TODO
+- [kotlin-asyncapi: Maven plugin and Spring Boot executable JAR scripting hosts](https://github.com/OpenFolder/kotlin-asyncapi)
 
 ## License
 The Apache 2 license (given in full in [LICENSE.txt](license/LICENSE.txt) applies to all code in this repository which