docs: add comprehensive README with features, setup, and usage

[loganlinn]

Summary

• Adds a detailed and visually appealing README for the dotfiles repository
• Introduces badges for FlakeHub, Nix Flake, and Home Manager
• Provides an overview of features, structure, and quick start instructions
• Details key components, theming options, and platform-specific features
• Includes customization guidelines, available commands, contributing steps, and resources
• Clarifies licensing and project motivation

Changes

Documentation

• Badges: Added status badges for FlakeHub, Nix Flake, and Home Manager
• Introduction: Added project tagline and description
• Features: Listed cross-platform support, Nix flakes, Home Manager, terminal setup, development tools, and modular design
• Project Structure: Outlined directory layout for configurations
• Quick Start: Step-by-step installation and usage instructions for NixOS, macOS, and home-manager
• Key Components: Described desktop environments, terminal and shell tools, development tools, and applications included
• Theming: Listed available color schemes
• Platform-Specific Features: Detailed configurations for NixOS, macOS, and Windows
• Customization: Instructions for forking, modifying, testing, and applying changes
• Commands: Provided just commands for common operations
• Contributing: Steps for contributing to the repository
• Resources: Links to relevant manuals and projects
• License: Added license information

Test plan

• Verified markdown formatting and link correctness
• Confirmed badge URLs and images render properly
• Checked command examples for accuracy
• Reviewed content for clarity and completeness

🌿 Generated by Terry

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📎 Task: https://www.terragonlabs.com/task/8b1f6e1d-169e-4ba3-a950-26e88c04cddb