Use Case: Make it clear how data entities and RepositoryObjects interact

[ptsefton]

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As a service/tools implementer I want clear advice about how to package data that comes from or is destined for a repository-like service organized with abstract collections and objects so that I don't make the mistake of leaving out links from the root dataset to Files content.

Easiest way to do this is to suggest that implementes put data in (eg) a files directory linked from the root dataset with hasPart links to File entities.

Suggest adding a note here: https://www.researchobject.org/ro-crate/1.1/data-entities.html