Modify demo site address (#443)

* Add workflow bpmn file preview support

* Adjusting the home page

* Modify demo site address

README.cn.md

@@ -37,7 +37,7 @@
 ### 在线体验
 > 请善待公共服务，会不定时停用
 
-地址：[https://kkview.cn/preview/index](https://kkview.cn/preview/index)
+地址：[https://file.kkview.cn](https://file.kkview.cn)
 
 ### 项目文档（Project documentation）
 1. 详细wiki文档：https://gitee.com/kekingcn/file-online-preview/wikis/pages

README.md

@@ -39,7 +39,7 @@ URL：[https://kkview.cn](https://kkview.cn/)
 ### Live demo
 > Please treat public service kindly, or this would stop at any time.
 
-URL：[https://kkview.cn/preview/index](https://kkview.cn/preview/index)
+URL：[https://file.kkview.cn](https://file.kkview.cn)
 
 ### Contact Us
 > We will answer your questions carefully and solve any problems you encounter while using the project. We also kindly ask that you at least Google or Baidu before asking questions in order to save time and avoid ineffective communication. Let's cherish our lives and stay away from ineffective communication.