generate a mips squashfs with some s6-rc services

haven't even tried booting it but I don't expect it to work. Needs

- s6-linux-init or some other pid 1 program
- a kernel

default.nix

@@ -0,0 +1,21 @@
+{ device ? (import devices/gl-ar750.nix)
+}:
+
+let
+  overlay = import ./overlay.nix;
+  nixpkgs = import <nixpkgs> ( device.system // {overlays = [overlay]; });
+  config = (import <liminix-config>) {
+    config = {
+      systemPackages = [];
+      services = {};
+    };
+    tools = nixpkgs.pkgs.callPackage  ./tools {};
+    inherit (nixpkgs) pkgs;
+  };
+  finalConfig = config // {
+    packages = (with nixpkgs.pkgs; [ s6-rc ]) ++
+               config.systemPackages ++
+               (builtins.attrValues config.services)
+    ;
+  };
+in (import ./make-image.nix) nixpkgs finalConfig