add the missing rust.musl-root option in config.toml.example
add the missing rust.musl-root option in config.toml.example

aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust