doc: note update of Ruby on Rails 6.0 packages:

devel/ruby-activesupport60
devel/ruby-activemodel60
databases/ruby-activerecord60
devel/ruby-activejob60
devel/ruby-activestorage60
devel/ruby-railties60
mail/ruby-actionmailbox60
mail/ruby-actionmailer60
textproc/ruby-actiontext60
www/ruby-actioncable60
www/ruby-actionpack60
www/ruby-actionview60
www/ruby-rails60

(taca)