Kudo’s for taking on this project! I just finished reading the forum thread from the person who lost valuable data, so I understand what motivated you to put together an FAQ for new users.
I believe that Syncthing is transitioning from a geeky project aimed at IT professionals into a widely-used consumer product. We should anticipate that in the future, a higher number (and percentage) of new users will not read the manual, and will not understand that sync/mirroring isn’t a substitute for file and folder backup.
In addition to improved readme and FAQ docs, I would also challenge us to think of ways that the application itself can be mistake-proofed. The goal: to eliminate undesired data loss.
Here’s one example: Ship Syncthing with versioning enabled (default), and design the UI so that a new user would likely have to look at the manual/FAQ to learn how to disable it.
I am sure there are better ideas out there.