Add Stakpak to docs about available agents

Author: ahmedhesham6

README.md

@@ -28,6 +28,8 @@ Learn more at [agentclientprotocol.com](https://agentclientprotocol.com/).
 - [Gemini](https://github.com/google-gemini/gemini-cli)
 - [Goose](https://github.com/block/goose)
   - [via Goose's acp command](https://block.github.io/goose/docs/guides/acp-clients)
+- [Stakpak](https://github.com/stakpak/agent)
+  - [via Stakpak's acp command](https://github.com/stakpak/agent?tab=readme-ov-file#agent-client-protocol-acp)
 
 ## Libraries and Schema