在中国大陆cargo命令速度很慢，怎么办？
使用如下配置：
# Put the content into ${HOME}/.cargo/config
[source.crates-io]
registry = "https://github.com/rust-lang/crates.io-index"
# replace with your favourite mirror
replace-with = 'sjtu'
[source.ustc]
registry = "git://mirrors.ustc.edu.cn/crates.io-index"
[source.sjtu]
registry = "https://mirrors.sjtug.sjtu.edu.cn/git/crates.io-index"
[source.rustcc]
registry = "https://code.aliyun.
