Document supported versions

[joshuap]

This gem depends on Postgres and Rails. Would be good to put that in the README (with tested versions).

[chrisedington]

Agree with this, saw it only supports Rails 5.2+ :(

[joshuap]

@chrisedington 5.2 through 6.1 currently. All versions of Rails prior to 5.2 are no longer receiving security updates. https://guides.rubyonrails.org/maintenance_policy.html

[johnknapp]

Might also mention the dependency on ActiveRecord. We prefer Sequel but will be fine with AR. But we wouldn't have wasted time with the wrong ORM if that was in the readme. :-)