git learning

 1. https://w3c.hexschool.com/git/7b64aa34

2. https://git-scm.com/book/zh-tw/v2/Git-%E5%9F%BA%E7%A4%8E-%E5%8F%96%E5%BE%97%E4%B8%80%E5%80%8B-Git-%E5%80%89%E5%84%B2