update document

doc/XXL-JOB官方文档.md

 执行器组件，配置内容说明：
 
 ```
-@Bean(initMethod = "start", destroyMethod = "destroy")
+@Bean
 public XxlJobSpringExecutor xxlJobExecutor() {
     logger.info(">>>>>>>>>>> xxl-job config init.");
     XxlJobSpringExecutor xxlJobSpringExecutor = new XxlJobSpringExecutor();