Fix php-curl-class#36: Add example of case-insensitive access to headers

Author: zachborboa

README.md

@@ -87,6 +87,14 @@ $curl->setOpt(CURLOPT_ENCODING , 'gzip');
 $curl->get('https://www.example.com/image.png');
 ```
 
+```php
+// Case-insensitive access to headers.
+$curl = new Curl();
+$curl->get('https://www.example.com/image.png');
+echo $curl->response_headers['Content-Type'] . "\n"; // image/png
+echo $curl->response_headers['CoNTeNT-TYPE'] . "\n"; // image/png
+```
+
 ```php
 $curl->close();
 ```