Add reference to Citrus simulator Spring Boot starter

Closes gh-10382

Author: christophd

spring-boot-starters/README.adoc

@@ -43,6 +43,9 @@ do as they were designed before this was clarified.
 | Charon reverse proxy
 | https://github.com/mkopylec/charon-spring-boot-starter
 
+| https://citrusframework.org/[Citrus] simulator
+| https://github.com/christophd/citrus-simulator
+
 | https://cloudant.com/[Cloudant]
 | https://github.com/icha024/cloudant-spring-boot-starter