What do we think people will use this space for? Stuff like "Post three times a week," "Write in the third person," etc.? Or stuff like "No violence against pets allowed in this game" or "No PC to PC romance"?
If it is the former, then that would be "Posting Guidelines." If it is the latter, then it would be something like "Table Agreement" or "Contract." None of that strikes me as "House Rules," though someone could use it for such (e.g. "No third-party material requests will be approved.")
If it is "all of the above," then I'd give it a very generic name like: "Game Expectations."