Update README.md

[glenn-jocher]

Add permanent splash URL and update hyperlink from iOS landing page to Ultralytics YOLOv5 landing page at https://ultralytics.com/yolov5

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Updated YOLOv5 documentation with new branding image and link.

📊 Key Changes

• Changed the main image in the README from an older version to a new splash image.
• Updated the link associated with the image to point to the Ultralytics YOLOv5 product page instead of the Apple App Store.

🎯 Purpose & Impact

• Visual Upgrade: Refreshes the project's README with a modern appearance, giving a better first impression to those discovering the repository.
• Corrected Resource Linking: Redirects users to a more relevant page (Ultralytics YOLOv5 page) that provides comprehensive information about the product, increasing visibility and user engagement.
• Potential Impact: Enhances the project's appeal and accessibility, which may contribute to increased adoption and community growth.

[glenn-jocher]

@kalenmike I've added splash.jpg now to our assets as discussed.