I don't think there's any super-detailed documentation. I think so far that most users fall into one of two categories:
1) just click buttons until they get something they like, export it, and use it in their games.
2) those already somewhat familiar with L-systems that just poke around a bit to translate my names into something they understand.
This is the entire extent of the existing documentation:
https://github.com/Simsilica/SimArboreal-Editor/wiki...other than what I posted on the jMonkeyEngine forums when I first announced it.
So, yeah, it could definitely use some better docs. On the other hand, no one is clamoring for them, either... but one could beget the other, really.
I guess I'll be picking your brain soon, then.
I'll try my best to document what I can based on intuition, first, of course. I have a good sense of about 1/4 or 1/3 of the options.
Oh, and uh... The j3o format is a touch restrictive, in that it can't be exported to another format. Perhaps it would be more popular if it could also export in another format... Though I don't know if that's even possible given my admittedly narrow understanding JME outside of the fact that j3o is a format used in JME. I guess the leaves wouldn't work in other formats either.