docs: document dumi dev server port

Author: afc163

README.md

@@ -100,6 +100,8 @@ npm run compile
 npm run build
 ```
 
+The dumi site runs at `http://localhost:8000` by default.
+
 ## Release
 
 ```bash

README.zh-CN.md

@@ -100,6 +100,8 @@ npm run compile
 npm run build
 ```
 
+dumi 站点默认运行在 `http://localhost:8000`。
+
 ## 发布
 
 ```bash