Add simple examples that queries 10 out of the top 500 domains

examples/benchmark.php

@@ -0,0 +1,23 @@
+<?php
+
+require __DIR__ . "/../vendor/autoload.php";
+
+use Amp\Dns;
+use Amp\Loop;
+
+$domains = file_get_contents("https://moz.com/top500/domains/csv");
+$domains = array_map(function ($line) {
+    return trim(explode(",", $line)[1], '"/');
+}, array_filter(explode("\n", $domains)));
+
+Loop::run(function () use ($domains) {
+    for ($i = 0; $i < 10; $i++) {
+        $domain = $domains[mt_rand(0, count($domains) - 1)];
+
+        try {
+            yield Dns\resolve($domain);
+        } catch (Dns\ResolutionException $e) {
+            print $domain . ": " . get_class($e) . PHP_EOL;
+        }
+    }
+});