clone 某个分支：
git clone -b b1 https://github.com/...
clone所有分支
git clone https://github.com/...
git branch -r
* master
origin/HEAD -> origin/master
origin/master
origin/b1
git checkout b1
clone 某个分支：
git clone -b b1 https://github.com/...
clone所有分支
git clone https://github.com/...
git branch -r
* master
origin/HEAD -> origin/master
origin/master
origin/b1
git checkout b1
