It’s better to use (init-server) to init GNU Artanis.
(init-server #:statics '(png jpg jpeg ico html js css) #:cache-statics? #f #:exclude '())
#:statics specifies the static files with the extension file. GNU Artanis is based on URL remapping, so this keyword let you avoid to handle each static file types. In default, it covers the most static file types. So you may ignore it usually.
#:cache-statics? indicates if the static files should be cached.