Add nix shell with development dependencies

shell.nix

@@ -0,0 +1,10 @@
+{ pkgs ? import <nixpkgs> {} }: pkgs.mkShell {
+  nativeBuildInputs = with pkgs; [
+    quilt
+
+    (python3.withPackages (ps: with ps; [
+      httplib2
+      six
+    ]))
+  ];
+}