Add quick start guide for new contributors

[SanjanaS10]

This PR adds a short "Quick Start for New Contributors" section to the README
to clarify workspace setup and common development commands.
No code changes are included.

[madhavajay]

Hi @SanjanaS10 I am interested to know what you would like to contribute to Biovault, maybe we can have a chat on slack?
https://openmined.org/slack/
#community-biovault

[SanjanaS10]

Hi @madhavajay ,

I’m still a beginner and fairly new to Biovault and OpenMined, so my main goal right now is to learn the codebase and understand the project better. While setting things up, I found the initial onboarding a bit challenging, which is why I thought improving the quick start guide could help other new contributors like me.

As of now, I’m mostly interested in:

• Documentation and onboarding improvements
• Beginner-friendly issues that help me get familiar with the workflow
• Small tasks in Python/Rust where I can learn while contributing

I’ll join the #community-biovault Slack channel soon. Looking forward to learning more and getting your guidance on how I can contribute.

Thank you
Sanjana

[SanjanaS10]

Fixed the quick start instructions to use ./repo --init