chore: adjust NixOS install instructions, add contributor

[RdrSeraphim]

Hey again!

Forgive me for this PR, but the instructions provided for NixOS use nix-env, which is largely considered an anti-pattern because it can cause a ton of conflicts between your system and what the Nix configuration declares. It's sort of a relic of the package manager from way back when and unfortunately it gets promoted as the de-facto way of installing packages by some places because it is the most analogous to something like sudo {apt,dnf} install.

https://stop-using-nix-env.privatevoid.net/ if you want to know the whole spiel :P

This provides the ideal instructions for installing the package, along with a note on having the package in a temporary shell for those with commitment issues who just need the programs for a moment.

Apologies, I should've provided more context in my email. I've had nix-env bite me in the past with something as simple as neovim, so just trying to avoid any future headache for people on Nix.

Thank you!

[craftablescience]

Oops