To reflect what was announced in prisma/prisma#3834 we need to show a warning to users calling prisma generate whenever their schema is using a provider array, like provider = ["sqlite", "postgres"] or similar.
The warning could link to the issue prisma/prisma#3834 to provide more context.

Suggested copy:

Warning: your schema is using the multiple datasource providers feature, which is now deprecated. We encourage you to use a single provider as this won't be supported in an upcoming release. You can read more about that in this issue: prisma/prisma#3834