Add a missing example for a case currency changing use case
Add a missing example for a case currency changing use case

This illustrates that the amount is preserved in units when currency is
changed to a different subunit/unit ratio. The example is controversial
and confusing, this commit just ensures that is covered by specs.

BookBub/money-rails,BookBub/money-rails,RubyMoney/money-rails,antstorm/money-rails,antstorm/money-rails,RubyMoney/money-rails,antstorm/money-rails,RubyMoney/money-rails,BookBub/money-rails