docs: add Setup Keys / PAT guide with API rename workaround

Document Setup Keys concept vs SSO, PAT creation and usage, and the
workaround for renaming a setup key — the API silently ignores the
name field on PUT, so the fix is to UPDATE store.db directly and
restart netbird-server.

README.md

@@ -16,6 +16,7 @@
 | [QUICKSTART.md](./QUICKSTART.md) | 快速部署步驟（適合複製貼上執行） |
 | [netbird-selfhosted-setup.md](./netbird-selfhosted-setup.md) | 完整安裝指南（含原理說明） |
 | [npm-grpc-fix.md](./npm-grpc-fix.md) | 透過 Nginx Proxy Manager 對外公開時的 gRPC 修復 |
+| [setup-keys-and-pat.md](./setup-keys-and-pat.md) | Setup Keys 概念、PAT 用法、以及 API 無法改名的繞道做法 |
 | [SUMMARY.md](./SUMMARY.md) | 部署摘要與疑難排解記錄 |
 
 ## 快速開始