Add nix build for reference

.github/workflows/nix.yml

@@ -0,0 +1,23 @@
+name: NixOS/nix
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+  schedule:
+    - cron: '0 9 * * 1'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: cachix/install-nix-action@v20
+      with:
+        nix_path: nixpkgs=channel:nixos-unstable
+    - uses: DeterminateSystems/magic-nix-cache-action@v2
+    - run: nix build .
+    - run: ls -lah result/bin/
+    - run: sha256sum result/bin/repro-env
+    - run: result/bin/repro-env --help

flake.nix

@@ -0,0 +1,22 @@
+{
+    inputs = {
+        flake-utils.url = "github:numtide/flake-utils";
+        naersk.url = "github:nix-community/naersk";
+        nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    };
+
+    outputs = { self, flake-utils, naersk, nixpkgs }:
+    flake-utils.lib.eachDefaultSystem (system:
+        let pkgs = (import nixpkgs) {
+            inherit system;
+        };
+
+        naersk' = pkgs.callPackage naersk {};
+
+        in rec {
+            defaultPackage = naersk'.buildPackage {
+                src = ./.;
+            };
+        }
+    );
+}