Chapter 15: NIX_PATH is no longer defined by default on non-NixOS

[noamraph]

Regarding https://nixos.org/guides/nix-pills/15-nix-search-paths#the-path-to-repository

Now NIX_PATH has a default. The document says to echo $NIX_PATH, but now it's no longer set by default. And this is no longer correct:

The NIX_PATH variable is exported by nix.sh, and that's the reason why I always asked you to source nix.sh at the beginning of my posts.

Configuration reference: https://nixos.org/manual/nix/stable/command-ref/conf-file#conf-nix-path