Hi Everyone,
We started working on a way for you all to create new levels about four weeks ago, and what we're bringing to you in a coming update is a simple, first, rough implementation of a way to make new levels and publish them on Steam Workshop.
There will be a Level Editing Guide under the Guides section, and the tools will be available after that.
When, you ask? Uhh.... soon™.
Please join the discussion on the announcement forum thread!