Add "Why Contribute" Section

# 🌟 Add "Why Contribute" Section

## 📌 Summary
Add a section explaining why users should contribute to this repository.

## ✨ Changes
- Add "Why Contribute?" section in README
- Highlight beginner benefits

## 🎯 Goal
Increase motivation and engagement for new contributors.

## ✅ Checklist
- [ ] Section added
- [ ] Content is beginner-friendly