Add CONTRIBUTING.md to Guide New Contributors

[SIDDHI-1105]

Hi maintainers 👋

I’ve been exploring the otpauthentication project — it’s a really useful FastAPI + Twilio-based OTP login system! 🙌

To make the repository more contributor-friendly and maintainable, I’d like to suggest adding a CONTRIBUTING.md file that outlines clear steps for contributing to the project.

✨ Suggested Contents for CONTRIBUTING.md:
📥 How to clone and set up the project locally

🔐 How to configure Twilio credentials securely (e.g., via .env)

🚀 Running the FastAPI server

🧪 Writing tests (if applicable)

🛠 How to create and submit a pull request (PR)

📄 Any code style, formatting, or branch naming conventions

✅ Good first issues or beginner-friendly contribution areas

✅ Why This Matters:
Lowers the barrier for new contributors

Encourages clean, consistent contributions

Saves maintainer time by answering common setup questions

Boosts project visibility and community involvement

I’d be happy to draft and contribute the initial CONTRIBUTING.md file myself if you'd like! Just let me know if you have any specific preferences you'd want included.

[DivyaJain-DataAnalyst]

Hello @Harish-2003

Can you please assign this issue to me if it is opened..