Fix contributions link in API bindings docs
Fix contributions link in API bindings docs

Closes #286

Sinar/popit,openstate/popit,Sinar/popit,mysociety/popit,mysociety/popit,mysociety/popit,openstate/popit,Sinar/popit,mysociety/popit,mysociety/popit,openstate/popit,Sinar/popit,openstate/popit