Nexus is right.
Yes, envelop classes for SFML doesn't make much sense because it's interface is already simple. But that doesn't mean you should use sf namespace, specially if you're going to put code on the wiki, because we indirectly assume that sf namespace means the code is part of the SFML library.
It's like the std namespace, you probably use the standard C++ directly to build your own generic and "standard" functionalities, however you don't use std namespace for your own code.
So you can use SFML directly and still have your own distinguishable namespace, like pd (from panithadrum)