Add php example

URL-signing.md

@@ -91,7 +91,7 @@ data = 'https://octodex.github.com/images/codercat.jpg'
 print base64.urlsafe_b64encode(hmac.new(key, msg=data, digestmod=hashlib.sha256).digest()) 
 ```
 
-### JavaScript
+## JavaScript
 
 ```javascript
 import crypto from 'crypto';
@@ -102,11 +102,16 @@ let data = 'https://octodex.github.com/images/codercat.jpg';
 console.log(URLSafeBase64.encode(crypto.createHmac('sha256', key).update(data).digest()));
 ```
 
-### PHP
+## PHP
 
 ````php
 <?php
 $key = 'test';
 $data = "https://www.google.fr/images/srpr/logo11w.png";
 echo strtr(base64_encode(hash_hmac('sha256', $data, $key, 1)), '/+' , '_-');
+````
+
+````shell
+$ php ex.php
+RYifAJRfbhsitJeOrDNxWURCCkPsVR4ihCPXNv-ePbA=
 ````