Fix discord social image URL

[glenn-jocher]

copilot:all

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Update of Discord logo links in README files.

📊 Key Changes

• Corrected the Discord logo image URLs to point to the 'raw' content links instead of the 'blob' in the English README.md.
• Made the same URL update to the Discord logo links in the Chinese README.zh-CN.md.

🎯 Purpose & Impact

• 📈 Enhances the visual consistency and reliability of the README files by ensuring the Discord logos are properly displayed.
• 🌐 Improves the user experience for GitHub users by fixing broken image links, potentially increasing community engagement on the Ultralytics Discord channel.