[Bug] Dataset Requirements list discrepancy with details

[SusanEarleyNASA]

Name: Susan Earley

Affiliation: NASA

Type of issue: Schema

Issue:
https://infopolicy.github.io/dcat-us/#properties-for-dataset - lists Identifier as Recommended.
https://infopolicy.github.io/dcat-us/#dataset-identifier - lists Identifier as Mandatory

This discrepancy is confusing.

Recommended change(s): Update the properties list to show Identifier as Mandatory.

[jbrown-xentity]

While this is a little different since the documentation disagrees with itself (and not the JSON schema), this should probably be taken on along with the cleanup work in #39 . Or we could implement new documentation based on the JSON schema definitions themselves...