Add flake and envrc.

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

.envrc

@@ -0,0 +1 @@
+use flake

flake.nix

@@ -0,0 +1,29 @@
+{
+  description = "Go dev shell";
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    systems.url = "github:nix-systems/default";
+    flake-utils = {
+      url = "github:numtide/flake-utils";
+      inputs.systems.follows = "systems";
+    };
+  };
+
+  outputs =
+    { nixpkgs, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          packages = with pkgs; [
+            go
+            gotools
+            gopls
+          ];
+        };
+      }
+    );
+}