Add example for worker thread

examples/worker-thread.php

@@ -0,0 +1,27 @@
+#!/usr/bin/env php
+<?php
+require dirname(__DIR__).'/vendor/autoload.php';
+
+use Icicle\Concurrent\Worker\TaskInterface;
+use Icicle\Concurrent\Worker\WorkerThread;
+use Icicle\Coroutine;
+use Icicle\Loop;
+
+class HelloTask implements TaskInterface
+{
+    public function run()
+    {
+        echo "Hello!\n";
+        return 42;
+    }
+}
+
+Coroutine\create(function () {
+    $worker = new WorkerThread();
+    $worker->start();
+
+    $returnValue = (yield $worker->enqueue(new HelloTask()));
+    yield $worker->shutdown();
+});
+
+Loop\run();