Update README.md (#510)

* Update README.md

* Update README.zh-CN.md
diff --git a/README.md b/README.md
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 Dashboard for [Apache APISIX](https://github.com/apache/apisix)
 
-[Online demo](http://139.217.190.60/)
+[Online Demo](http://139.217.190.60/), Username/Password: `admin`.
 
 ## User Guide
 
diff --git a/README.zh-CN.md b/README.zh-CN.md
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 [Apache APISIX](https://github.com/apache/apisix-dashboard) 的仪表盘
 
-[在线演示](http://139.217.190.60/)
+[在线演示](http://139.217.190.60/),账户密码:`admin`。
 
 ## 用户指南