How to serve static files WebApp2 NO Google AppEngine

I am trying to use WebApp2 outside of AppEngine and can't find anywhere in the documentation how to set up static routes to files.

For example, I have the following folder structure

Presentation

-->js
-->-->main.js
-->templates
-->-->index.html (loaded via Jinja)

How do I reference the main.js as using ../js/main.js gives me a 404