Improvement to docs for send_file function

src/Control/HTTPRequest.php

@@ -468,6 +468,8 @@ class HTTPRequest implements ArrayAccess
      * Construct an HTTPResponse that will deliver a file to the client.
      * Caution: Since it requires $fileData to be passed as binary data (no stream support),
      * it's only advisable to send small files through this method.
+     * this function needs to called inside the controllers response, eg
+     * $this->setResponse(HTTPRequest::send_file('the content', 'filename.txt'));
      *
      * @static
      * @param $fileData