You might want to try not telling them, but introduce it but by bit into the bedroom once your relationship gets to that stage.
Start by using a tie to bind their wrists to the headboard and tease them or let them come home to you bound as such, whichever is your preference. Even if someone hasn’t tried it out before, they might be a little more inclined to give it a go, and who knows, they might even enjoy it.
It’ll be up to you to decide how big a step your willing to take with them at the time, but don’t go from a gentle tease with their wrists bound to hardcore bdsm bondage gear for hours on end, but slowly build up to it. They’ll let you know when they start feeling uncomfortable and then you’ll know the relationships limit.
Hope this helped
Darkside94