Readme comment on Ruby 3 + Rails 6.1

[alishersadikov]

This is not a bug report but a report of a potentially misleading Readme comment. The Readme says Ruby 3 is supported only on Rails 6.1, but I think it is also supported on Rails 6.0.1. Maybe the Readme statement was accurate at some point in the past?

https://rubygems.org/gems/rails/versions/6.0.1

And:
https://www.fastruby.io/blog/ruby/rails/versions/compatibility-table.html

Also left a comment on the relevant PR: #734 (comment)