update document

xxl-job-core/src/main/java/com/xxl/job/core/handler/annotation/JobHandler.java

@@ -9,6 +9,7 @@ import java.lang.annotation.Target;
 /**
  * annotation for job handler
  *
+ * will be replaced by {@link com.xxl.job.core.handler.annotation.XxlJob}
  *
  * @author 2016-5-17 21:06:49
  */