Add an example for leader election based multiple controller

examples/leader_example/mix.exs

@@ -0,0 +1,25 @@
+defmodule LeaderExample.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :leader_example,
+      version: "0.1.0",
+      elixir: "~> 1.6",
+      deps: deps()
+    ]
+  end
+
+  def application do
+    [
+      extra_applications: [:logger, :libcluster, :locks, :tres],
+      mod: {LeaderExample.Application, []}
+    ]
+  end
+
+  defp deps do
+    [{:locks, "~> 0.2.0"},
+     {:libcluster, "~> 2.3.0"},
+     {:tres, path: "../../../tres"}]
+  end
+end