Update CONTRIBUTING.md file

[milevavantuyl]

The CONTRIBUTING.md file doesn't have instructions on the workflow for contributing to the repo.

• Add the process for forking the repo
• Branching
• Creating a PR
• And merging in the changes

[natnichalerdwa]

Hi, I would like to do this. Please assign it to me.

[natnichalerdwa]

I have opened a PR for this issue. Please review and approve. Thank you!