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

[Programmer-RD-AI]

Updated Hello World Code Sample in README.md

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

Why Are These Changes Needed?

The Hello World example in the README.md file does not properly await the agent.run() method, leading to a RuntimeWarning. This fix ensures the example demonstrates correct usage of the library, providing a better experience for users following the documentation.

Related Issue Number

Closes #5012

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See [Contribute Documentation](https://microsoft.github.io/autogen/docs/Contribute#documentation) to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[ekzhu]

Thank you!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.60%. Comparing base (9f351c5) to head (344afbd).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5013   +/-   ##
=======================================
  Coverage   68.60%   68.60%           
=======================================
  Files         156      156           
  Lines       10053    10053           
=======================================
  Hits         6897     6897           
  Misses       3156     3156           

Flag	Coverage Δ
unittests	68.60% <ø> (ø)

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