Comprehensive README.md rewrite for improved clarity, structure, and accessibility

[Copilot]

Overview

This PR delivers a complete rewrite of the README.md to significantly improve documentation clarity, structure, and accessibility for both new users and contributors. The new documentation provides a more professional and beginner-friendly experience while maintaining all technical depth.

Key Improvements

🎯 Enhanced Introduction & Overview

• Professional badges: Added GitHub Actions build status and Apache 2.0 license badges
• Clearer value proposition: Expanded introduction explaining import-tree's purpose and benefits
• Better positioning: Connected the tool to the Dendritic Pattern concept upfront

📋 "Features at a Glance" Section

New organized feature overview with categorized highlights:

• 🚀 Easy to Use - One-liner imports, flake-ready, zero dependencies
• 🎯 Universal Compatibility - Works across all major Nix module systems
• 🔧 Highly Customizable - Extensible API, smart filtering, transformations
• 📦 Library-Friendly - Pre-configured trees, community conventions

🚀 Restructured Usage Examples

• Separate quick starts for flake and non-flake users
• Enhanced code examples with comprehensive comments and explanations
• Basic usage patterns for different scenarios (NixOS, home-manager, etc.)
• Progressive complexity from simple to advanced use cases

📚 Improved Documentation Structure

• Removed collapsible sections for better accessibility and discoverability
• New "Understanding the Default Behavior" section explaining file discovery and ignore patterns
• Comprehensive API Reference with clear method documentation and examples
• Better headings hierarchy for easier navigation

🔧 Enhanced Technical Content

• Detailed API explanations with practical examples for each method
• Custom API extension examples showing real-world library distribution patterns
• Better code comments throughout all examples
• Enhanced "Why" section with deeper explanations of benefits and use cases

🧪 Improved Testing & Contributing Sections

• Updated testing instructions with current commands and structure
• New comprehensive Contributing section with:
  • Development setup guide
  • Code style guidelines
  • Testing requirements
  • Submission process

Before vs After

Before: The README had a basic structure with important API documentation hidden in collapsible sections, making it less accessible to newcomers.

After: The README now provides a clear learning path from basic usage to advanced customization, with all important information easily discoverable and well-organized.

Benefits

1. Better onboarding for new users with clear quick start guides
2. Improved discoverability of advanced features through better organization
3. Enhanced professional appearance with badges and structured formatting
4. Comprehensive contributor guidance to encourage community participation
5. Maintained technical depth while significantly improving accessibility

The documentation now serves as both an effective introduction for newcomers and a comprehensive reference for experienced users, fulfilling the goal of creating more beginner-friendly and professional documentation.

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[vic]

I'm not merging this because you removed my tree emojis from the title!