need to add trusted-users options in /etc/nix/nix.conf for home-manager users

[junyi-hou]

For people who do not use nixOS, I need to run
sudo echo "trusted-users = $(whoami)" >> /etc/nix/nix.conf to enable cacheix substitution and public key defined in ~/.config/nix/nix.conf.

Also, it would be good to include a warning on the security issues associated with this (as indicated in the manual here)

[jonascarpay]

I added note and a link to this issue to this issue in the README.

Note that this also applies to people who run NixOS, but in that case you just add your own username to the nix.trustedUsers system option.

[junyi-hou]

Thanks!