Add Contribution guidelines.

[atarax665]

Add CONTRIBUTING.md File

As this project is a part of an Open Source Program NJACK Winter of Code I would recommend to have a contribution guidelines file (CONTRIBUTING.md) to assist beginners to get started with open source contribution.

Points to be covered in the guideline :

• How to pull your first request.
• How to create issue.
• Some general rules to keep in mind while contributing to an open source project.
• Links of some tutorials which will help beginners to learn the basics of git and github.

[Pranav016]

I would be happy to help add Contributing guidelines for first time contributors.

[AkbarHabeeb]

Feel free to add @Pranav016