Add beforeSend example

examples/multi_curl_before_send.php

@@ -0,0 +1,23 @@
+<?php
+require __DIR__ . '/vendor/autoload.php';
+
+use \Curl\MultiCurl;
+
+$headers = array(
+    'Content-Type' => 'application/json',
+    'X-CUSTOM-HEADER' => 'my-custom-header',
+);
+
+$multi_curl = new MultiCurl();
+
+$multi_curl->beforeSend(function ($instance) use ($headers) {
+    foreach ($headers as $key => $value) {
+        $instance->setHeader($key, $value);
+    }
+});
+
+$multi_curl->addGet('https://www.example.com/');
+$multi_curl->addGet('https://www.example.org/');
+$multi_curl->addGet('https://www.example.net/');
+
+$multi_curl->start();