To use the overlay

Add the overlay to your home.nix (home-manager) or configuration.nix (nixos):

{
  nixpkgs.overlays = [
    (import (builtins.fetchTarball {
      url = https://github.com/nix-community/neovim-nightly-overlay/archive/master.tar.gz;
    }))
  ];
}

If you are using flakes to configure your system, add to your nixpkgs overlays attribute (examples will differ, the following is for home-manager):

{
  inputs.neovim-nightly-overlay.url = "github:nix-community/neovim-nightly-overlay";
  outputs = { self, ... }@inputs:
    let
      overlays = [
          inputs.neovim-nightly-overlay.overlay
        ];
    in
      homeConfigurations = {
        macbook-pro = inputs.home-manager.lib.homeManagerConfiguration {
          configuration = { pkgs, ... }:
            {
              nixpkgs.overlays = overlays;
            };
        };
      };
}

Note, I recently switched the overlay to use flakes by default with flakes-compat for older nix. Please report issues if this breaks things.

Install neovim-nightly:

nix-env -iA pkgs.neovim-nightly

or add to home-manager/configuration.nix.

Binary cache

You will want to use the nix-community binary cache. Where the overlay's build artefacts are pushed. See here for installation instructions.