Update releases URL in README

[pderrenger]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Refinement of model download instructions in the iOS app README.

📊 Key Changes

• Updated the URL for downloading YOLOv8 CoreML INT8 models to point directly to the releases page.

🎯 Purpose & Impact

• Purpose: To make the process of acquiring pre-trained models for the YOLO iOS app more straightforward.
• Impact: Users will have a clearer guide and direct access to the necessary model files, potentially reducing confusion and streamlining the app setup process. 📲🛠️