Added passthru streaming example

examples/stdin_streaming_stdout.php

@@ -0,0 +1,24 @@
+<?php
+
+use kamermans\Command\Command;
+
+require_once __DIR__.'/../vendor/autoload.php';
+
+$filename = __DIR__.'/../README.md';
+$stdin = fopen($filename, 'r');
+
+// This will read README.md and grep for lines containing 'the'
+$cmd = Command::factory("grep 'the'")
+    ->setCallback(function($pipe, $data) {
+        // Change the text to uppercase
+        $data = strtoupper($data);
+
+        if ($pipe === Command::STDERR) {
+            Command::echoStdErr($data);
+        } else {
+            echo $data;
+        }
+    })
+    ->run($stdin);
+
+fclose($stdin);