I looked at Telltale’s web pages for a demo version, and some Google results said there was one available, but I could not find a simple “Here, download episode one for free!” link or button. :(
It’s a shame that I now have to download an illegal, cracked episode one version from sites like ddl-warez with my paid Share-Online account just to see if it is worth to buy the full legal version. That’s the thing which keeps pirating alive.

(Generally it would be nice to have demo versions on GOG, if available.)