You'll need diet, housing (and exercise) and health info, along with info on specific illnesses rabbits in general are prone to and ones they will be prone to because of their genetics or breed. You'll also need info on vaccination and neutering and I would make this a requirement of rehoming them as well - draw up a contract. I imagine you are rehoming them only in pairs or as a companion for another rabbit, but I would put in some info on companionship and bonding. I'd also include a list of rabbit-savvy vets in the area.
I'd also include a few of the key RWAF leaflets.