I actually have found the check-in instructions very handy, even before I had self check-in I had the check-in instructions filled in with pictures and description on how to walk to the apartment from the nearest train station as its not always straight forward.
I have now extended it to include how to self check-in.
You can only create it on your mobile, however if you go to your inbox and go to message, there is a little key icon, these are the check-in instructions that you can send to the guest yourself.
This is only available through mobile app, although once you send these to 1 guest, you can copy and paste the link to other guests from your desktop too.