Upgrade instructions incomplete when doing v7 => v8

[clemoun]

Bug Report

Describe the Bug:
Incomplete upgrade instructions to go from version 7 to 8

To Reproduce:
The current paragraph suggests that running
rails pay:install:migrations
rails db:migrate
is enough

But if you already are on Pay 7, several migrations installed by rails pay:install:migrations would be duplicates

Solution:
The paragraph should just state :
run rails pay:install:migrations
then delete the migration timestamp_create_pay_tables.pay.rb => The file is not necessary if you are already in pay-rails v7
then run rails db:migrate

Could be obvious for good developers but not "meh" ones like me.
Sorry, I don't even know how to contribute to the project and push this change myself....