Improve README.md - Githubissues

@pderrenger changes to Ultralytics landing page as recommend. Please review!

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

New welcome message added to Ultralytics GitHub profile page emphasizing AI model offerings and community engagement.

Added a welcoming introduction that outlines Ultralytics' focus areas: detection, segmentation, classification, tracking, and pose estimation.
Invited contributions and provided links for community interaction, such as feature requests and bug reports.
Mentioned the availability of state-of-the-art AI models in the Ultralytics repository.
Encouraged joining the mission to democratize AI.

🎉 Enhances community awareness regarding the scope of Ultralytics' work and expertise in AI.
👍 Encourages open-source collaboration, potentially leading to better models and more robust software.
🚀 Invites users and developers to contribute, fostering a more active and diverse community which can propel innovation further.
🌐 Makes AI more approachable and usable for developers and organizations, solidifying Ultralytics' role as a leader in AI solutions.