feat: Add shell.nix for running a local Nixery

shell.nix

@@ -0,0 +1,27 @@
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Configures a shell environment that builds required local packages to
+# run Nixery.
+{pkgs ? import <nixpkgs> {} }:
+
+let nixery = import ./default.nix { inherit pkgs; };
+in pkgs.stdenv.mkDerivation {
+  name = "nixery-dev-shell";
+
+  buildInputs = with pkgs;[
+    jq
+    nixery.nixery-build-image
+  ];
+}