Add minimal shell.nix to use with nix package manager and direnv file

which can be activated just with direnv or lorri

.envrc

@@ -0,0 +1,5 @@
+if has lorri; then
+  eval "$(lorri direnv)"
+else
+  use nix
+fi

shell.nix

@@ -0,0 +1,11 @@
+{ pkgs ? import <nixpkgs> { } }:
+
+with pkgs;
+
+mkShellNoCC {
+  buildInputs = [
+    autoconf
+    automake
+    gnumake
+  ];
+}