Contribution Guideline

- [x] Branch Policy
- [x] [Coding Standard](https://github.com/guitar-academy/gaclient/issues/2)
- [x] Testing
- [x] Developer Documentation
- [x] Contribution Guide

Anything else?
CSS indentation follows JS and not HTML?
Also, for JS, is the indentation 4-space tab or 4 spaces (like, real spaces)?