Best practices for IRI identifiers

[balmas]

I don't know if this would be considered in scope for this effort, but it would be really helpful to have a set of recommended best practices for IRI identifiers used for linguistic annotations. E.g. when/if to use ARKs vs Handles vs DOIs, vs PURLs.

[chiarcos]

I add a separate section on best practices to required-features.md and add it there. Not sure whether this isn't too broad, but there clearly is a need. I keep the issue open to capture any discussion of the topic.