[New user experience]: No mention of `export method` can be confusing when trying to setup Beta distribution

[taquitos]

No export method option being mentioned in https://docs.fastlane.tools/getting-started/ios/beta-deployment/. When running fastlane beta, it seems that fastlane defaults to using iOS Distribution provisioning profiles if export_method is not set to 'development'.

Let's make that more clear

[KrauseFx]

Great idea 👍