docs: add comprehensive README for Library Management System

[YogeshwaranOfficial]

Summary

This pull request adds a comprehensive README for the Library Management System project.

Changes Included

• Added detailed project overview and feature list
• Added technology stack documentation for frontend and backend
• Added project architecture overview
• Added installation and local development setup instructions
• Added environment variable configuration guide
• Added API documentation section
• Added testing instructions for unit and integration tests
• Added CI/CD workflow documentation
• Added deployment placeholders for Frontend, Backend, Database, and API Documentation
• Improved project onboarding experience for contributors and reviewers

Impact

• Improves project documentation and maintainability
• Makes local setup easier for new developers
• Provides a central reference for project architecture and workflows
• Helps future deployment and collaboration efforts

Testing

Documentation-only changes.
No application code was modified.