Add reference to Casdoor Spring Boot Starter

See gh-30220

spring-boot-project/spring-boot-starters/README.adoc

@@ -64,6 +64,9 @@ do as they were designed before this was clarified.
 | https://camunda.org/[Camunda BPM]
 | https://github.com/camunda/camunda-bpm-spring-boot-starter
 
+| https://casdoor.org/[Casdoor]
+| https://github.com/casdoor/casdoor-spring-boot-starter
+
 | Charon reverse proxy
 | https://github.com/mkopylec/charon-spring-boot-starter