README is empty — add basic project overview + quickstart

[priyan17singh]

Title: Add a basic README for onboarding (project overview + quickstart)

Body:
Hi maintainers 👋

The repository README is currently minimal, so it’s hard for new contributors to understand what EXXA contains and how to start.

What I’m proposing

Add a small README.md that includes:

• a 1–2 line project overview
• a list of top-level approach folders
• a minimal quickstart (clone → venv → open Jupyter)
• a short note that datasets/dependencies vary by folder

Why this helps

This improves onboarding/discoverability without changing any code or assumptions about datasets.

If you’re okay with it, I can open a PR with the README update.
Thanks!

[yoginlangalia]

I have opened a PR to address this: #17

The new README includes a project overview, a directory structure table describing all 10 sub-projects, getting started instructions, related GSoC 2026 project list, contributing guidelines, and acknowledgments.