Deprecate this repo/gem

[cllns]

In a chat @fractaledmind, you said:

"If you are using Rails 8, you don't need the enhanced adapter at present. Rails 8 is out-of-the-box ready for production with SQLite"

It might help people out to add a note to the top of the README saying this gem is for use with Rails 7.2 and isn't necessary for Rails 8.

You could also archive it, to get the yellow banner at the top that might help people see it's not necessary for current/future Rails projects.

[matthewblott]

@cllns I've been including this gem in my Rails 8 projects by habit. I know it isn't strictly necessary but I did think there might be the benefit of some added features. Is this not the case? If so then yes, I agree it should say that it's for Rails 7 and below on the homepage :-)