README Documentation does not cover many important options and direct configuration

[theirishpenguin]

Thanks for all your work on this package @drewolson. I'm just opening this ticket (and will supply have supplied a pull request with a fix) to improve the libary's documentation.

The Problem

The README does not mention options such as :allow_overflow_page_number and direct configuration such as :max_page_size

Maybe some of this configuration should be described in scrivener rather than scrivener_ecto - but that can be figured out. First, I'd like to ensure that a complete set of options is knowable to end users.