Add OpenClaw to clients list in documentation (#585)

Author: ignatov

docs/get-started/clients.mdx

@@ -28,6 +28,7 @@ The following clients can be used with an ACP Agent:
   - through the [yetone/avante.nvim](https://github.com/yetone/avante.nvim) plugin
 - [Obsidian](https://obsidian.md)
   - through the [Agent Client](https://github.com/RAIT-09/obsidian-agent-client) plugin
+- [OpenClaw](https://docs.openclaw.ai/tools/acp-agents)
 - [Sidequery _(coming soon)_](https://sidequery.dev)
 - [Tidewave](https://tidewave.ai/)
 - [Toad](https://www.batrachian.ai/)