Update v5 migration guide (#570)
Update v5 migration guide (#570)

* In section on 3DS, make the comments for each integration method (CocoaPods, Carthage, SPM) collapsible so that the guide is easier to read

* Add section on changes to 3DS delegate method

* Add note about Braintree/Apple-Pay subspec being renamed to Braintree/ApplePay
braintree/braintree_ios,braintree/braintree_ios,braintree/braintree_ios,braintree/braintree_ios