docs: add sonarcloud badge to readme, fix #34

Author: zambrovski

README.md

@@ -2,6 +2,7 @@
 
 [![Maven Central](https://maven-badges.herokuapp.com/maven-central/org.axonframework.extensions.kotlin/axon-kotlin/badge.svg)](https://maven-badges.herokuapp.com/maven-central/org.axonframework.extensions.kotlin/axon-kotlin)
 [![Open Source Helpers](https://www.codetriage.com/axonframework/extension-kotlin/badges/users.svg)](https://www.codetriage.com/axonframework/extension-kotlin)
+[![SonarCloud Gate Status](https://sonarcloud.io/api/project_badges/measure?project=AxonFramework_extension-kotlin&metric=alert_status)](https://sonarcloud.io/dashboard?id=AxonFramework_extension-kotlin)
 
 _Note:_ This extension is still in an experimental stage.