Add example Nix file

example.nix

@@ -0,0 +1,15 @@
+{pkgs}:
+rec { a = [ 1 2 3 ]; b = { b1 = true; b2 = { b21 = 1; really-really-long-name = { b221 = "foo"; b22 = [ 1 2 3 4 5 6 7 8]; }; }; };
+  c = f {
+    inherit a; str = ''#! ${pkgs.stdenv.shell}\n echo "Hello!"\n'';
+    environment.systemPackages = with pkgs; [ tmux vim ];
+  };
+    d = let tool = "nixfmt"; in "${tool} is awesome";
+e = let lots = "lots";
+             of = "of";
+                 binds = "binds";
+                    which = "which";
+                        were = "were";
+                            originally = "originally";
+                                unaligned = "unaligned"; in "wow!";
+}