Add blog post: MongoDB Compound Indexes and Multi-Field Query Optimization

Comprehensive tutorial on MongoDB compound indexes covering:
- Advanced multi-field indexing strategies
- Query optimization and performance tuning
- Index intersection and effectiveness analysis
- SQL-style compound index operations with QueryLeaf
- ESR rule and best practices for index design
- Performance monitoring and optimization recommendations

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: rathboma