This page talks about being able to set the schema attribute used for the entitlement’s description but does not indicate what needs to be updated on the schema to make that happen
The description isn’t mapped correctly in the source schema. To view your current mapping, submit an API call using Lists Schemas on Source. If the mapping is incorrect, you can submit an API call using the Update Source Schema (Partial) endpoint to alter the group schema’s description attribute.
This post describes how to make that happen which I think should be added to the documentation page.