Consider clarifying meaning of required vs. optional information

[sdruskat]

Currently, cffinit provides information in the breadcrumb about what information is required vs optional in terms of producing a valid CFF file. This is good, but it's slightly misleading for users that want to provide minimally required or even all recommended metadata for their software with respect to the software citation principles.

The latter argues for a larger set of information as being required for good practice.

It would be great to make this distinction clear somehow, although I don't know a good way to implement this. One idea could be to introduce an extra marker for fields that are recommended, in addition to required?

This could also be part of #710 perhaps?