Add headscale-piying web UI to docs

docs/ref/integration/web-ui.md

@@ -19,5 +19,6 @@ Headscale doesn't provide a built-in web interface but users may pick one from t
   it offers Local (`docker exec`) and API Mode
 - [headscale-console](https://github.com/rickli-cloud/headscale-console) - WebAssembly-based client supporting SSH, VNC
   and RDP with optional self-service capabilities
+- [headscale-piying](https://github.com/wszgrcy/headscale-piying) - headscale web ui,support visual ACL configuration
 
 You can ask for support on our [Discord server](https://discord.gg/c84AZQhmpx) in the "web-interfaces" channel.