Airbnb has nothing to say about it. It's absolutely your right to put it up as long as it's legal. As a matter of fact I know many hosts put this in their description, although I have no weed rule in my house rules. Depending on how much you want to advertise, you can put it in your title and description.
Something Airbnb should have something to say is to those who violate the house rule. I have had several guests used weed in my listings while I clearly stated no weed. Airbnb is not helping at all.
