title: Line Bot subscribeing with parameter?
body: <p>Line Bot API Service provied an QRcode for subscribing an channel. Onece User subscribed, the server shell get the subscribed event.
  It' seems stupid that telling user to send their user_id in the line channel to link the Line user id.
  Is there any way to add parameter to the QRCode for subscribing, such like the user_id, So Bot Server  can recevie it for link the user?</p>