Contribution Guide 필요

Contribution Guide에 대한 설명이 부족합니다

[예시1](https://github.com/Microsoft/calculator/blob/master/CONTRIBUTING.md)
[예시2](https://github.com/naver/claf/blob/master/CONTRIBUTING.md)
Contribution Guide 샘플 템플릿
[Google Open Source Contrubuting Sample](https://github.com/google/new-project/blob/master/CONTRIBUTING.md)
