git learning:

1. git config --global user.name "xxx"
   git config --global user.email "xxxx"
   
   
2. git init
   git add filename
   git commit -m "comment text"
   git status
   
3. git diff filename   
   git log
   
4. git reset --hard version/HEAD
   git reflog
   
5. 工作区和版本库(workSpace, Repository)

6. git checkout --filename //撤销工作区的修改