前提：mac上已经安装homebrew
1、使用如下命令：
brew install git
brew会自动去下载安装git
2、等待安装结束，出现如下提示：
==>Downloading https://homebrew.bintray.com/bottles/git-2.18.0.sierra.bottle.ta
######################################################################## 100.0%
==>Pouring git-2.18.0.sierra.bottle.tar.gz
==>Caveats
Bash completion has been installed to:
/usr/local/etc/bash_completion.d
zsh completions and functions have been installed to:
/usr/local/share/zsh/site-functions
Emacs Lisp files have been installed to:
/usr/local/share/emacs/site-lisp/git
==>Summary
🍺 /usr/local/Cellar/git/2.18.0: 1,488 files, 296.8MB
如下所示，git安装在/usr/local/Cellar下
