Update Ultralytics YouTube URL

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced YouTube link for automatic subscription prompt.

📊 Key Changes

• Updated the YouTube link in the README to include a subscription prompt.

🎯 Purpose & Impact

• Engagement Boost: Including a "?sub_confirmation=1" query in the YouTube URL encourages visitors to subscribe, potentially increasing Ultralytics' YouTube channel subscriptions 📈.
• User Convenience: This change simplifies the process for visitors who wish to stay updated with Ultralytics content, making it a one-click action to subscribe 🖱️.
• Community Growth: A higher subscription rate enhances community engagement and growth, fostering a larger audience for Ultralytics' updates and announcements 🌍.