chore: update the readme for a2a integration (#319)

chore: update the readme for a2a integration

Author: hangfei

README.md

@@ -112,6 +112,9 @@ adk eval \
     samples_for_testing/hello_world/hello_world_eval_set_001.evalset.json
 ```
 
+## 🤖 A2A and ADK integration
+
+For remote agent-to-agent communication, ADK integrates with the [A2A protocol](https://github.com/google/A2A/). See this [example](https://github.com/google/A2A/tree/main/samples/python/agents/google_adk) for how they can work together.
 
 ## 🤝 Contributing