Use /etc/zshenv instead of /etc/zshrc for profile
Use /etc/zshenv instead of /etc/zshrc for profile

As noted in https://github.com/NixOS/nix/issues/3456 the `/etc/zshenv` file provides a better place for sourcing the nix environment.
rycee/nix,NixOS/nix,rycee/nix,NixOS/nix,NixOS/nix,rycee/nix,NixOS/nix,rycee/nix,rycee/nix,NixOS/nix