adding nix shell development environment, tested

default.nix

@@ -0,0 +1,13 @@
+{ nixpkgs ? import <nixpkgs> {  } }:
+
+let
+  pkgs = [
+    nixpkgs.go
+    nixpkgs.tmux
+  ];
+
+in
+  nixpkgs.stdenv.mkDerivation {
+    name = "env";
+    buildInputs = pkgs;
+  }