Prompt to set document type as root if there is no root document type

[devantler]

When starting new Umbraco projects and creating document types, it would be nice to get a prompt on save that asks if the document type should be allowed as root. Ideally, this should happen if no existing document type is set as root.

I think this could make it a bit easier to create content for new users, who might not be aware of the requirement of allowing document types as root to use the document type to create root content nodes 🤘🏻