Rust 配置中科大的下载源

在~/.cargo下创建文件config(注没有后缀)并添下如下内容:

[registry]
index = "https://mirrors.ustc.edu.cn/crates.io-index/"
[source.crates-io]
replace-with = "ustc"
[source.ustc]
registry = "https://mirrors.ustc.edu.cn/crates.io-index/"