Update README.md

[ItsMeStevieG]

Added addition information about creating long life tokens

[ItsMeStevieG]

Perhaps add this here, or alternatively consider starting a USAGE.md and add a few examples such as $api->getServices() and maybe show some functional example such as $api->getCustomer() and $api->getCustomer()->getEmail() to show how to access elements within each scope.

Also an additional suggestion, maybe elaborate on what the scopes actually give access to.