Improve UI (at least online help) related to encryption and master keys

[thatman]

I think the app would benefit if some points from this thread could be implemented, even without changing the code - just having a better wording would help a lot.

Of course, more extensive changes would help even more, but that maybe unnecessary

Concrete suggestions can be found in the original comment here:

Struggling with Sync setup -- too much searching

Thanks dpoulton. This is something that should be clearly mentionned in the help page (or did I missed it ?). Because I know nothing about all this stuff, and I was under the impression that encryption had to be activated on every device... and that's what I did