Updated schema.md

[dsmorgan77]

This pull request has been automatically generated by prose.io.

[dsmorgan77]

"System of Records" has a specific meaning under the Privacy Act of 1974. A link to the system is not recommended. In all cases, systems of records will likely be designated as "restricted" data in the accessLevel field of the schema, as the Privacy Act of 1974 specifically limits disclosure. However, the System of Records Notice (SORN) associated with a system of records provides instructions on how to request records from such a system. Therefore, it is most appropriate to link to the SORN.

[jpmckinney]

+1 to clarify the meaning of this property, which I requested in #49. Would be good to add a few words to the "Rationale for Metadata Nomenclature" about systemOfRecords to say that it a new term introduced by this project.

[haleyvandyck]

Thanks @dsmorgan77--good clarification.