added FAQ on limits and conscious departure as optimization

the phrasing is still a bit awkward, so this is merely intended to start the discussion

would appreciate input from @stilkov, @tillsc, @cdent and whoever else might care

aside: I tried to work what I consider a powerful quote from @cdent into this, but it didn't quite fit in. Any ideas where we might put it:

> ROCA is a distillation of ten years of web development experience.
> An example of a situation where ROCA doesn't quite fit might be a good idea here.

I'd considered that, but that seemed tricky without turning this FAQ into a lengthy article...