Add NixOS shell config

Via rust-windowing/glutin#642

Author: rsaarelm

default.nix

@@ -0,0 +1,6 @@
+let
+   pkgs = import <nixpkgs> {};
+in pkgs.stdenv.mkDerivation rec {
+  name = "glutin-env";
+  LD_LIBRARY_PATH = with pkgs.xlibs; "${pkgs.mesa}/lib:${libX11}/lib:${libXcursor}/lib:${libXxf86vm}/lib:${libXi}/lib:${libXrandr}/lib";
+}