I'm struggle with the same problem, trying to integrate my game to steam, but sadly there is no real step-by-step tutorial for greenworks at all...
I'm wondering if I need to do something specific in C2 to get the steam overlay running or do I just need to follow the steps of the greenworks documentation which are only applied AFTER exporting the NW.js and it will work automatically?
So far I added the greenworks object to my project and set up "greenworks is available"+trigger -> "Activate Achievement : ACH_ID" in C2. But are there other things to do inside C2 to get greenworks running? Like what about the overlay? Do I now just need to export and follow the steps of the greenworks documentation afterwards?
Help please, I'm so confused! ;O