Improve README: Better structure, environment setup, and installation clarity

[dipgarg0011]

📘 Summary

This pull request updates the README.md to make it more structured, beginner-friendly, and production-ready.
The goal is to improve clarity for new contributors and learners following the MERN E-Commerce tutorial.

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✨ Improvements Made

🔹 Enhanced Structure

• Added clear sections: Features, Tech Stack, Installation, Project Structure, Tutorials, etc.
• Improved formatting for better readability.

🔹 Environment Setup Added

• Added complete config.env template.
• Explained each required variable (MongoDB, JWT, Cloudinary, SMTP, Stripe).

🔹 Installation Instructions

• Clear step-by-step setup for backend and frontend.
• Proper project tree included.

🔹 Professional Tone & Developer-Friendly Layout

• More readable headings, spacing, and icons.
• New contributor-friendly guidelines.

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🧪 Tested

• Verified Markdown formatting.
• Ensured no breaking changes to the codebase (README only).

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🙌 Purpose

This PR helps:

• Beginners learning MERN
• Contributors setting up the project quickly
• Maintainers improve documentation quality

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✔️ Ready to Merge

No code changes — documentation only.