Update README.md to main branch

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced project setup guide in README.

📊 Key Changes

• Updated the link in the README.md to point to the requirements.txt in the main branch instead of the master.

🎯 Purpose & Impact

• Simplifies Setup: Ensures users access the correct, up-to-date dependencies needed for the project.
• Consistency: Aligns with GitHub's naming conventions, making it easier for users new and old to set up their development environment.
• Accessibility: Helps avoid confusion and streamlines the process for users to get started with the COCO2YOLO project, potentially increasing user adoption and satisfaction.

[sourcery-ai]

We have skipped reviewing this pull request. We don't currently review documentation changes - Let us know if you'd like us to change this.