Update README.md to main branch

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improved the repository by updating image links and enhancing documentation clarity.

📊 Key Changes

• Updated image links in the README from master branch to main branch.
• These changes make sure the images are displayed correctly by pointing to the correct branch in the repository.

🎯 Purpose & Impact

• Accuracy: Ensures all users can see the relevant images, improving the readability and user experience of the documentation.
• Up-to-date Information: Reflects the GitHub naming convention shift from master to main, showing the project's adherence to current standards.
• User Experience: Enhancements in documentation lead to better understanding and easier setup for new users, potentially increasing adoption and positive feedback.

🖼️ These updates ensure users have visual aids to successfully navigate and use the project, making the project more accessible and user-friendly.