Provide examples for provenance metadata (including more complex nested examples)

[jbusecke]

I am finding myself totally winging the population of the provenance section of pgf recipes at LEAP.

I think it would be very helpful to have a page demonstrating the following things:

• What is the set of roles that we thing are valid (maybe should be checked in the schema?)
• How to encode organizations vs authors (e.g. Jane Do at NOAA produced this dataset, what role should be commonly associated with NOAA vs Jane)
• How do we encode nested provenance. Maybe this breaks the data model of PGF, but I have an example here(PR) where a researcher at leap has produced a dataset from another original dataset. We would like to acknowledge everyone who participated in this effort. What do folks here think is the best way to do this?

Happy to provide the docs once we have had a discussion on the details.