so the functionality to claim Steam Keys has just been deployed to the website. If you have a promotional or paid membership (Transport Belt Repair Man or higher) then you can claim a Steam key on your profile page. There is a section dedicated to Steam Access as can be seen below on the screenshot.
Simply clicking the button will generate a Steam key for you. You can then copy paste the generated key and use it via the Steam app to activate the game. The game will be released on Thursday 25th Feb 2016 at 11:00 a.m. PST. Only after this date will it actually be possible to get the game via Steam. We thought it would be possible to write reviews already, but unfortunately that doesn't seem to be the case=( The amount of keys is limited for now to 20000. In case these run out or are close to running out we will request a new batch from Steam. So Enjoy!
There is a thread for comments if you need it at our forums.