It's OK. I think the FAQ could probably be promoted a little more and maybe structured a little differently. You're not the first by far to have trouble finding it, either.
A couple days ago I tried searching Google to find it with a few common things (like "roundcube spellcheck problem") and it wasn't listed on the first few pages. It is listed now, so I'm not sure what changed.
Anyhow, it's good to hear that your problem is fixed!
Jim