Improve README

[pderrenger]

This pull request attempts to improve the repo README file with additional context and content.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced 'ultralytics/assets' repository with updated branding, streamlined content, and clarified licensing options.

📊 Key Changes

• 🆕 Introduced new Ultralytics logo and removed the old banner image.
• ✏️ Rewrote the introductory text to be more engaging and informative.
• 🖼️ Added an image of open-source contributors.
• 🔏 Detailed two licensing options: AGPL-3.0 for open-source use and an Enterprise License for commercial applications.
• 🧰 Simplified the example code snippet for using pre-trained models.
• 📑 Provided clear instructions for downloading and using datasets.
• 🎨 Updated the social media icons and adjusted their layout for aesthetic improvements.

🎯 Purpose & Impact

• 🖌️ Refocusing the brand image reflects a fresh and modern approach to Ultralytics' public representation.
• 📈 Enhanced readability and new contributor showcase can increase community engagement.
• 📋 Clarifying the licensing terms ensures users can easily choose the right license for their needs, potentially expanding the user base.
• 💾 Streamlining code examples aids in ease of use for developers leveraging Ultralytics models.
• 🌐 Refreshed social links reinforce the online presence and accessibility of the Ultralytics team.