Nix run renaming

[tomberek]

NixOS/nix#3551

This will need to be updated in your Makefile at some point.
nix run -> nix shell

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[saschagrunert]

NixOS/nix#3551

This will need to be updated in your Makefile at some point.
nix run -> nix shell

Hey, thank you for the hint. Do you wanna propose a PR if the changes got released? :)