如何配置 ~/.gitconfig 文件而不是单个 repo 的 .git/config 文件?
## use this config if repository belongs to userA@github
[user]
name = userA
email = userA@gmail.com
## use this config if repository belongs to userB@github
[user]
user: userB
email: userB@yahoo.com
## use this config if repository belongs to userC@bitbuck
[user]
user: userC
email: userC@hotmail.com