[scr_ecto-103] Improve options/configuration described in README

[theirishpenguin]

The Problem

The README does not mention options such as :allow_overflow_page_number and direct configuration such as :max_page_size. This is noted in issue #103

This PR is to (make a start at least) on correcting that.

[theirishpenguin]

One check fails above with the following error...

Is there something I should do to correct this?

(As this is just a documentation change, I'm conscious it's probably best if I don't go messing with the actual codebase as part of this PR 😄 )

[theirishpenguin]

A fellow Elixir-er kindly helped me out with the build issue at https://github.com/theirishpenguin/scrivener_ecto/pull/1/files

Looking at that PR, it seems like there is an issue building scrivener_ecto with elixir: '1.15.0' / otp: '26.0.1'. I guess that this means that an update will be needed for scrivener_ecto to keep it building on otp: '26.0.1'. I might open an issue on this repo to call this out explicitly. (Given the Low Maintenance warning on this repo, I guess you won't have time to work on this actively @drewolson - which is understandable).