Provide a section on reordering entities

[laijasmine]

Rearrange file order alphabetically:

1. metadata:

   doc$dataset$otherEntity <- doc$dataset$otherEntity[order(entity_names)]

2. datafiles (using arcticdatautils):

   pkg <- get_package(adc, rm, file_names = T)
   doc <- EML::read_eml(getObject(adc, pkg$metadata))
   reordered <- arcticdatautils::reorder_pids(pkg$data, doc)

• while re-ordering the groups of entities is possible manually, it isn't possible the way write_eml and publish_update is written. This is not recommended.