Improve README - Githubissues

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

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

Revamped .github repository introduction and resources description for better clarity and community engagement.

Updated the repository welcome message to emphasize its role as a central resource hub.
Enhanced descriptions for GitHub Actions Workflows, Issue, and Pull Request Templates to convey their benefits more clearly.
Defined Contributing Guidelines as a "backbone" for collaboration, emphasizing alignment with processes.
Shifted focus towards streamlining contributions for both Ultralytics team members and community contributors.
Added a contributors' image to recognize community engagement aesthetically.
Updated contact and community engagement instructions, encouraging the use of GitHub Issues and Discord chat for discussions.

To provide a more welcoming and informative entry point to the repository, aiding both the Ultralytics team and external collaborators.
Ensures that workflows and templates are better understood, leading to more efficient, consistent contributions.
Acknowledges the efforts of the community, potentially incentivizing more collaboration.
Aims to simplify the process of reporting issues or feature requests and participating in discussions, fostering a more vibrant community.