Add CONTRIBUTING.md

[DevrajDC]

• Include details about how to contribute on to this repo.
• Add git basic commands for beginners.
• Add how beginners can contribute to this repo.

[abhishekpatel946]

Hey, @DevrajDC is it still open or not? If it's open then you can assign it to me. I can work on it thanks!

[mRahulRoy]

Will pr count for fest?