title: Add comment/url to VCALENDAR
body: <p>I am looking for a way to specify a URL or comment in a icalendar file which will be shown by user agents in some sort of details or properties window.
  (Emphasis on being shown by user agents)</p>
  
  <p>I don't want to specify this for a single event but rather a whole <code>VCALENDAR</code> element.
  It should work with all common user agents.</p>
  
  <p>I'd like to use this to include a feedback URL/email address, that users can discover without having to inspect the raw file.
  (The ical files are the only communication channel I have)</p>