Clarify whether Type Of Content in Data File Descriptions is correct

[matthewhorridge]

It is possible that this should be "Description Type", which would be consistent with Datacite.

[graybeal]

I believe that was explicitly documented in the text description for those fields, at least once upon a time. ('Description Type' is a terrible name for it. When I have time to look it up I will confirm.

[matthewhorridge]

After chatting offline with @graybeal. This field should be the type for the description.

TODO: Add description to docs about how to fill out this field programmatically.