Provide nginx if [ -d ".nginx-conf" ]

Currently users are supposed to run their own HTTP WSGI server for
their Python application and they have to use this application if they
also want to serve static files or similar.

By creating the ".nginx-conf" directory, users now can trigger a build
of nginx. This allows them to create more advanced setups with different
locations, redirects, etc.
fixup! Provide nginx if [ -d ".nginx-conf" ]