Create CONTRIBUTING.md

[manaswinidas]

Create a CONTRIBUTING.md for helping contributors

Expected Behavior

README should give just run instructions and CONTRIBUTING should give instructions to introduce changes and to check whether the changes work

Current Behavior

There is a single README

Possible Solution

Context

It's difficult for contributors to find their way around unless they go through the whole code base.

Your Environment

• Version used:
• Environment name and version (e.g. Chrome 39, node.js 5.4):
• Operating System and version (desktop or mobile):
• Link to your project: