release.nix -> default.nix

the default should be to build all the images

pkgs.nix

@@ -0,0 +1,8 @@
+import <nixpkgs> {
+  # docker images run on Linux
+  system = "x86_64-linux";
+  config = {};
+  overlays = [
+    (import ./overlay.nix)
+  ];
+}