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. It depends on to what extent you want this to be helpful for overcoming that last 10% to get to 100%. If you just want to put the warning out there and leave the rest to the rest of the world, that's fine too.