Link local docs in Fauxton

@KlausTrainer noticed me on the yesterdays CouchDB Meetup that not the docs for the current version are linked, but instead the latest one online:

Instead of linking to the latest version online, we link to the
docs for the locally installed version. The docs are
generated automatically when running make / make install, if you
have Sphinx installed. For development, the dev-server will just
proxy the request.