Add Nix flake

flake-modules/dev-shell.nix

@@ -0,0 +1,18 @@
+{ inputs, ... }:
+
+{
+  imports = [
+    inputs.devshell.flakeModule
+  ];
+
+  perSystem =
+    { pkgs, ... }:
+    {
+      devshells.default = {
+        packages = with pkgs; [
+          go
+          gopls
+        ];
+      };
+    };
+}

flake-modules/systems.nix

@@ -0,0 +1,3 @@
+{
+  systems = [ "x86_64-linux" ];
+}