Add --source screen Usage example

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Added screenshot functionality to prediction tools for classification, detection, and segmentation.

📊 Key Changes

• Introduced the ability to use screenshots as a source for image classification (predict.py), object detection (detect.py), and segmentation (predict.py).

🎯 Purpose & Impact

• 🎉 Enhanced flexibility: Users can now directly use screenshots as input, making it more convenient to test the model with screen content.
• ✅ Better user experience: This reduces the steps needed to save and load screen content, streamlining the testing and deployment process.
• 🚀 Potentially wider applicability: This feature could be useful for real-time applications where capturing the screen content is necessary, such as in monitoring or streaming tasks.