Clarify docs about is_dynamic not being updated by set_config()

If you take a look at the set_config function, it only will set the is_dynamic on insert, but during update, it won't change it, so if code is changed to being dynamic, or not being, this is not updated.

Not sure if this is too much of a relevant bug, because I'm not sure if a user will ever have a problem with this because the code would probably not be changing after the config is set, but I thought I'd report this non-the-less.