added Groovy/Grails plugin reference restapidoc

Author: muenchhausen

README.md

@@ -80,6 +80,9 @@ These are third party tools generated by the Swagger community:
 - [beego](https://github.com/astaxie/beego) - A framework support support auto generate swagger spec from comments
 - [Swagger spec generator](https://github.com/yvasiyarov/swagger) - A swagger spec auto generator. Doesn't depends on any framework  
 
+#### Groovy
+- [restapidoc](https://github.com/emicklei/go-restful) - A simple RESTful API documentation plugin for the Grails web application framework.
+
 #### Java
 - [swagger-springmvc](https://github.com/martypitt/swagger-springmvc) - Integration with Spring MVC.
 - [swagger4spring-web](https://github.com/wkennedy/swagger4spring-web) - Integration with Spring MVC.