https://mirrors.tuna.tsinghua.edu.cn/help/nix-channels/
For warning when temporarily using a mirror via
--option substituters URL :
warning:
ignoring untrusted substituter 'https://mirrors.tuna.tsinghua.edu.cn/nix-channels/store', you are not a trusted user.
Run man nix.conf for more information on the substituters configuration option.
ref
https://discourse.nixos.org/t/adding-trusted-substituters-on-the-fly-when-running-nixos-rebuild/25486/2