docs: add quick start guide

docs/QUICKSTART.md

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+# Quick Start / 快速上手
+
+This guide helps new users install YAML Proxy Editor, open an existing Clash/OpenClash/Mihomo YAML file, refresh subscriptions, and export a usable configuration without changing the project source code.
+
+本文帮助新用户安装 YAML Proxy Editor、打开现有 Clash/OpenClash/Mihomo YAML、刷新订阅并导出可用配置，不涉及修改项目源码。
+
+## 1. Install / 安装
+
+Use one of the prebuilt Windows installers in the repository `release/` directory:
+
+使用仓库 `release/` 目录中的 Windows 安装包：
+
+- `release/YAML-Proxy-Editor-0.1.0-x64-setup.exe`
+- `release/YAML-Proxy-Editor-0.1.0-x64-zh-CN.msi`
+
+Choose the EXE installer for the common NSIS setup flow. Choose the MSI installer when you prefer Windows Installer based deployment.
+
+常规安装建议使用 EXE；需要 Windows Installer 部署流程时使用 MSI。
+
+## 2. Open A YAML File / 打开 YAML 文件
+
+1. Start YAML Proxy Editor.
+2. Open an existing OpenClash, Clash, Mihomo, or MetaCubeX YAML file.
+3. Review the left sidebar index to confirm proxies, proxy providers, rule providers, DNS, and OpenClash sections were recognized.
+4. Keep a backup of important production configuration before saving changes.
+
+1. 启动 YAML Proxy Editor。
+2. 打开已有 OpenClash、Clash、Mihomo 或 MetaCubeX YAML 文件。
+3. 在左侧索引确认节点、订阅源、规则源、DNS 和 OpenClash 配置被正确识别。
+4. 保存前请保留重要生产配置的备份。
+
+## 3. Refresh Subscriptions / 刷新订阅
+
+Subscription refresh is user-triggered. The app should not upload local YAML files or automatically contact unknown domains.
+
+订阅刷新必须由用户主动触发；应用不应上传本地 YAML，也不应自动访问未知域名。
+
+Recommended flow:
+
+推荐流程：
+
+1. Import or define provider URLs in the subscription page.
+2. Run provider checks only for URLs you trust.
+3. Refresh subscriptions when you want to update proxy nodes.
+4. Review warnings before writing changes back to the YAML file.
+
+## 4. Export / 导出
+
+After editing or refreshing, export the configuration format required by your client:
+
+编辑或刷新后，按客户端需要导出：
+
+- Clash / Mihomo YAML
+- OpenClash provider YAML
+- Share-link subscriptions for supported clients
+- Base64 subscription text when required by downstream tools
+
+## 5. Related Docs / 相关文档
+
+- `docs/BUILD.md` explains local build steps.
+- `docs/TESTING.md` lists verification commands.
+- `docs/NETWORK_POLICY.md` documents network boundaries.
+- `docs/OFFLINE_SECURITY.md` explains local-first safety expectations.
+
+Before modifying source code, read `AGENTS.md` and keep creator identity, network boundaries, and release files unchanged unless the project owner explicitly requests otherwise.
+
+修改源码前请先阅读 `AGENTS.md`，除非项目所有者明确要求，否则不要改创作者信息、网络边界或 release 安装包。