Basic curl implementation

Please add it to the README.

```php
function curl_get_contents( $url ) {

if ( ! function_exists( 'curl_init' ) ) {
return false;
}

$ch = curl_init();
$timeout = 60;

curl_setopt( $ch, CURLOPT_URL, $url );
curl_setopt( $ch, CURLOPT_CONNECTTIMEOUT, $timeout );
curl_setopt( $ch, CURLOPT_RETURNTRANSFER, true );
$response = curl_exec( $ch );
curl_close( $ch );

return $response;
}

// Instantiate the Message and Validator
$message = Message::fromRawPostData();
$validator = new MessageValidator( 'curl_get_contents' );
```

Open the repository README and compare its current usage examples with the PHP curl snippet in this issue. Add the provided example in the appropriate usage section, preserving its formatting and context. Done means the README documents this curl-based setup clearly; no test file is mentioned in the issue.

Written by the indexing model from the issue text.