do not encourage use of nix-env

[fricklerhandwerk]

Beginners are consistently confused over nix-env, as it usually does not do what they want. Do not encourage it, provide declarative options instead.

Related:

• https://stop-using-nix-env.privatevoid.net/
• Anti pattern: imperative package management nix.dev#17
• https://discourse.nixos.org/t/depreciate-the-use-of-nix-env-to-install-packages/20139

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/usability-study-session-2/21400/1