Move around some files. Add ‘nix.el’ that is now the main entry point
to configurations. If you want the full experience of Nix integration
into Emacs, try running this (if you are already using use-package):

  (use-package 'nix
    :ensure 'nix-mode
    :demand
    :config (global-nix-mode))

Otherwise you can still do something like this:

  (use-package 'nix-mode
    :mode "\\.nix\\'"))

This avoids issues with exec-path conflicts

Used in nix-shell.el

This is a little bit easier to remember name.

This makes things easier to use.

Also nix-shell-file is risky

This can be used for completion

This isn’t very useful anyway.

This should be done elsewhere

This will hopefully be able to replace README.md

add more flags