Add a way to distinguish "submissionDocumentation" from "actual data"

[ptsefton]

It's been pointed out that the spec doesn't distinguish between supporting files contextualising the data and the actual research data parts of the package. Have a look at how to address this - how is this done in the archive/preservation community? Is there a way to model this in schema.org?

[ptsefton]

This should be considered in the Research Object Lite/Crate work. https://github.com/ResearchObject/ro-lite

Putting it in the backlog