docs: Improve README.md and CONTRIBUTING.md

[vj7-byte]

Summary

This pull request significantly enhances the README.md and CONTRIBUTING.md files to improve the developer experience for new users and contributors.

Key Improvements to README.md

• Added Quick Start Section: A minimal, self-contained C++ code example has been added to help new users get started with CacheLib quickly.
• Added Key Features Section: A clear, concise list of CacheLib's main features has been included to highlight its capabilities.
• Added "Why Use CacheLib?" Section: This new section explains the ideal use cases for CacheLib and helps users understand when it is the right choice.
• Added Architecture Overview: A high-level overview of CacheLib's architecture has been added to provide context for new contributors.
• Improved Build Instructions: The build and installation steps have been consolidated and clarified for a smoother setup process.
• Added Community Section: Links to GitHub Issues, Discussions, and Stack Overflow have been added to help users find support.

Key Improvements to CONTRIBUTING.md

• Added Documentation Contributions Section: Clear instructions have been added for contributors who wish to improve the documentation.
• Added Code Style Guidelines: A reference to the .clang-format file and code formatting expectations has been included.
• Added PR Template Information: The pull request process and template are now described to guide contributors.
• Improved Overall Clarity: The document has been reorganized for better readability.

These changes aim to make CacheLib more accessible and welcoming to both new users and potential contributors.

Test Plan

This is a documentation-only change. All code examples have been reviewed for correctness.

• Verified that the Quick Start code example is correct and compiles.
• Reviewed all new sections for clarity and accuracy.
• Checked all links to ensure they are valid.

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[meta-cla]

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