Valve has introduced several changes to how demos are handled on Steam, as well as how developers can better get them in front of potential players.
Perhaps the most notable addition is that studios can now set up separate store pages for their free demos, where they can post screenshots, trailers and specify the contents of this download. These pages will also automatically link to the full game's store page for wishlisting or purchase.
In the announcement post, Valve said these pages are optional and can be taken down at a later date if the developer chooses. Studios will need a full written description, screenshots and tags before a page can go live. Pages can be set up for demos already available on Steam.