I am not sure this is necessary, pragmatically the front page tells you what this site is about, and that statement may change with time. We can add some comments to the effect that we try to be inclusive and would welcome questions which stretch the definition of theoretical physics somewhat, but in all honesty we probably don't know the scope of this site yet -- it depends what the user base will end up being.
More specifically, I don't know that the existence of a question like
Rigorous security proof for Wiesner's quantum money?
would convince anyone in the Quantum Information and Foundations proposal that this is a good space for them. Any of the good arguments in that thread (e.g. the subject is interdisciplinary) or the bad ones (we don't want to rub elbows with those particle types) is an a priori argument not affected by evidence. I think it is already pretty difficult to look at our front page and come up with the impression that QI questions are not welcome here. In fact, at the moment QI research probably represents the majority of our user base.
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