Fix foreign-free example in the documentation.
Fix foreign-free example in the documentation.

akovalenko/cffi,dochang/cffi,marsijanin/cffi,dochang/cffi,cffi/cffi,wesen/cffi,stassats/cffi,attila-lendvai/cffi,kingcheez/cffi-cheez,dochang/cffi,kingcheez/cffi-cheez,wesen/cffi,3b/cffi,dkochmanski/cffi,3b/cffi,marsijanin/cffi,attila-lendvai/cffi,cffi/cffi,dkochmanski/cffi,akovalenko/cffi,kingcheez/cffi-cheez,cffi/cffi,dkochmanski/cffi,3b/cffi,marsijanin/cffi,wesen/cffi,mcna/cffi,akovalenko/cffi,stassats/cffi,mcna/cffi,stassats/cffi