Add AgentRank score badge to README

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Author: 2 people

README.md

@@ -39,6 +39,8 @@
 
 ## Quick Start
 
+[![AgentRank Score](https://agentrank-ai.com/api/badge/tool/CoplayDev--unity-mcp)](https://agentrank-ai.com/tool/CoplayDev--unity-mcp)
+
 ### Prerequisites
 
 * **Unity 2021.3 LTS+** — [Download Unity](https://unity.com/download)