Create comprehensive README documentation for coalesce.js library

[Copilot]

Transforms the minimal 2-line README into comprehensive documentation that makes the library easy to understand and use.

Changes Made

📚 Complete Documentation Added:

• Installation instructions with npm commands
• Basic usage examples for quick start
• Detailed API documentation with parameters, return values, and error conditions
• Extensive examples covering all JavaScript data types (numbers, strings, booleans, objects, arrays, functions)
• Practical use cases for configuration management, user data handling, and API response processing
• Edge cases documentation including error conditions and falsy value behavior
• Comparison with SQL COALESCE for familiarity
• Development section with testing, linting, and coverage instructions
• Contributing guidelines for open source collaboration
• Professional badges and proper attribution

🔍 Key Features Documented:

const { coalesce } = require('@everymundo/coalesce');

// Basic usage
coalesce(undefined, null, '', 'first truthy value'); // 'first truthy value'

// Configuration with fallbacks
const config = {
  port: coalesce(process.env.PORT, process.env.DEFAULT_PORT, 3000),
  host: coalesce(process.env.HOST, 'localhost')
};

// Edge cases clearly explained
coalesce(null, []); // [] (empty array is truthy)
coalesce(); // TypeError (no arguments)

✅ Quality Assurance:

• All 20+ code examples tested and verified to work correctly
• Existing tests continue to pass
• Code follows project linting standards (StandardJS)
• Documentation accurately reflects actual library behavior
• Comprehensive coverage of falsy vs truthy values in JavaScript

The library now has professional-grade documentation that transforms it from a minimal utility into a well-documented, discoverable package ready for broader adoption.

Fixes #15.

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