[TASK] add comment for addAttachment

Classes/Service/MailTemplateService.php

@@ -583,6 +583,8 @@ class MailTemplateService {
 	}
 
 	/**
+	 * IMPORTANT: make sure to set $this->>ignoreMailQueue(TRUE), if you're using this method to add an attachment!
+	 * Otherwise the attachment is ignored when sending the mail via mail queue.
 	 * @param Swift_OutputByteStream $data
 	 * @param string $filename
 	 * @param string $contentType