Docs: Enhance README.md for clarity and usability

[thesteganos]

This commit significantly revamps the main README.md to improve its clarity, visual appeal, and overall usefulness for both new and existing users.

Key changes include:

• Simplified language in introductory sections ("What is KAG?", "Core Features").
• Added an overview GIF to provide an immediate visual understanding of KAG.
• Inserted placeholders for future demo GIFs in the "Quick Start" section.
• Made the "Star our repository" call to action more prominent.
• Restructured the "Release Notes": summarized in README with a link to a comprehensive docs/release_notes.md.
• Added a new "Illustrative Examples" section, describing KAG's capabilities and linking to detailed examples in kag/examples/.
• Created a CONTRIBUTING.md file with basic guidelines.
• Added a "Contributing" section to the README, linking to the new guidelines.
• Performed a full review for grammar, spelling, formatting, link correctness, and sequential section numbering.