Add contributions guidelines

[barun-saha]

Update documentation to include style and other guidelines for contributions.

[sairampillai]

@barun-saha Let's also add a precommit hook so every commit is validated locally before committing

[barun-saha]

That's a good idea, @sairampillai. Do you think you can help with that as well?

[sairampillai]

Sure, will set it up and raise a PR