improve level 1 summary description

[azaroth42]

In: https://iiif.io/api/discovery/0.3/#listing-resources-and-their-changes

Level 1 adds timestamps and ordering from earliest change to most recent, allowing the consumer to stop processing once it encounters a change that it has already processed

is a bit confusing because while the pages go from earliest to most recent, the processing is in reverse. If we're to talk about processing, then we should also mention that order.

/ht @mixterj