Bring documentation inline with latest developments in `IndividualFacilityUse`

[nickevansuk]

As proposed in openactive/modelling-opportunity-data#218 (comment), the documentation should be improved to encourage the use of IndividualFacilityUse.

[nickevansuk]

Documentation and examples have been updated for expediency to aid the planning work of current implementers, however this issue remains open pending further discussion / reflection on openactive/modelling-opportunity-data#218 (comment)