docs: add admin-ui build instructions to README (#18)

* docs: add admin-ui build instructions to README

* Delete admin-ui/package-lock.json

---------

Co-authored-by: hank9999 <hank9999@qq.com>

README.md

@@ -24,6 +24,11 @@
 
 ## 快速开始
 
+> **前置步骤**：编译前需要先构建前端 Admin UI：
+> ```bash
+> cd admin-ui && npm install && npm run build
+> ```
+
 ### 1. 编译项目
 
 ```bash