You can't until you have an official reservation. Once you have a reservation, a unique, anonymous email address will be created you can use to send the additional information.
What is an official reservation? I have to instant bookings which I have approved but never received an "anonymous email address". Why is it annonymous? What does this mean? Why not just give their proper email address? It is all a bit creepy!
Can I send web links to the person through the email?