ARMv7 SD image

For clarity, this release was created by:

nix-build '<nixpkgs/nixos>' -A config.system.build.sdImage -I nixos-config='./sd-image_generic.nix'

where sd-image_generic.nix contains:

{ config, pkgs, ... }: {

  imports = [
    <nixpkgs/nixos/modules/installer/cd-dvd/sd-image-armv7l-multiplatform.nix>
  ];

  boot.kernelPackages = pkgs.linuxPackages_4_19;
}

and where my nixpkgs is based on git commit:

68aad7348a0eb90571daa9dd60f1aca6be962455