Update README.md to show rdagent in qlib front page

[peteryang1]

Description

Motivation and Context

How Has This Been Tested?

• Pass the test by running: pytest qlib/tests/test_all_pipeline.py under upper directory of qlib.
• If you are adding a new feature, test on your own test scripts.

Screenshots of Test Results (if appropriate):

1. Pipeline test:
2. Your own tests:

Types of changes

• Fix bugs
• Add new feature
• Update documentation

[RahulVadisetty91]

This README.md script is crucial for informing users about new features, releases, and documentation. A clean, structured, and well-linked README.md can improve user engagement and make the project easier to navigate, especially for new users