add message to exaplain how to use it

Author: 0xCardinalError

agent/src/index.ts

@@ -752,7 +752,7 @@ const startAgents = async () => {
     }
 
     elizaLogger.log(
-        "Run `pnpm start:client` to start the client and visit the outputted URL (http://localhost:5173) to chat with your agents"
+        "Run `pnpm start:client` to start the client and visit the outputted URL (http://localhost:5173) to chat with your agents. When running multiple agents, use client with different port `SERVER_PORT=3001 pnpm start:client`"
     );
 };