Fix: Properly await agent.run() in README Hello World example (microsoft#5013)

* Fix: Properly await `agent.run()` in README `Hello World` example

- Updated the `Hello World` code sample to use `asyncio` for proper coroutine handling.
- Resolved `RuntimeWarning` caused by not awaiting the `agent.run()` method.
- Ensures the example executes correctly without errors or warnings.

* Add await to agent.run call in index.md

* Fix hello world

---------

Co-authored-by: Eric Zhu <[email protected]>

Author: Programmer-RD-AI

README.md

@@ -34,7 +34,7 @@ from autogen_ext.models.openai import OpenAIChatCompletionClient
 
 async def main() -> None:
     agent = AssistantAgent("assistant", OpenAIChatCompletionClient(model="gpt-4o"))
-    print(agent.run(task="Say 'Hello World!'"))
+    print(await agent.run(task="Say 'Hello World!'"))
 
 asyncio.run(main())
 ```

python/packages/autogen-core/docs/src/index.md

@@ -119,7 +119,7 @@ from autogen_ext.models.openai import OpenAIChatCompletionClient
 
 async def main() -> None:
     agent = AssistantAgent("assistant", OpenAIChatCompletionClient(model="gpt-4o"))
-    print(agent.run(task="Say 'Hello World!'"))
+    print(await agent.run(task="Say 'Hello World!'"))
 
 asyncio.run(main())
 ```