Update documentation for model schema changes.
Update documentation for model schema changes.

mrpau/kolibri,learningequality/kolibri,indirectlylit/kolibri,indirectlylit/kolibri,indirectlylit/kolibri,mrpau/kolibri,indirectlylit/kolibri,learningequality/kolibri,learningequality/kolibri,mrpau/kolibri,learningequality/kolibri,mrpau/kolibri