add setup instruction to contributing guidelines

Author: krvajal

CONTRIBUTING.md

@@ -3,3 +3,12 @@
 You *always* want to look at this file **before** contributing. In here you
 should find steps that you need to take to set up your development environment
 as well as instructions for coding standards and contribution guidelines.
+
+
+## Setup instructions
+First of all, this is a Visual Studio Code extension that uses TypeScript and tools based on [Node.js](https://nodejs.org/en/) with dependencies from npm. So you will need to have Node installed on your `$PATH`. 
+1. Fork the repo
+2. Clone your fork
+3. Create a branch
+4. Run `npm install`
+