安装brew 报告找不到git，并因错误而终止。Brew 似乎已安装（成功？）
> brew
（打印通常的帮助）
...但brew doctor不高兴：
这是我运行brew doctor时得到的结果（以及当我按照Homebrew主页上的说明第一次安装brew时得到的结果。）
> brew doctor
Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry and just ignore them. Thanks!
Warning: Git could not be found in your PATH.
Homebrew uses Git for several internal functions, and some formulae use Git
checkouts instead of stable tarballs. You may …