R""(
Set the nixpkgs
flake identifier to a specific branch of Nixpkgs:
Pin nixpkgs
to a specific revision:
Add an entry that redirects a specific branch of nixpkgs
to another fork:
Add nixpkgs
pointing to github:nixos/nixpkgs
to your custom flake registry:
This command adds an entry to the user registry that maps flake reference from-url to flake reference to-url. If an entry for from-url already exists, it is overwritten.
Entries can be removed using nix registry
remove".
)""