Custom fields and field groups should include a description

Nili Steiner makes a good point about documenting one's custom fields to avoid duplication in this blog post: https://civicrm.org/blogs/nili/data-standardisation-creating-sound-data-plans-civicrm

It strikes me that most of the information Nili suggests including is already available in the Civi database. The only thing missing is a 'description' field for custom fields and custom field groups. With that, one could create a utility to automatically generate documentation.