Update information on how backup works #247
Description
With the migration to Gorilla imminent (looks like it'll start next service window, the 4th unless I'm mistaken?) and the switch from "backup-first-specify-nobackup" on Crex to "nobackup-first-specify-backup" on Gorilla, we're going to need to update https://docs.uppmax.uu.se/cluster_guides/backup/ . It is currently only mentioning the "old" style of users specifying when a directory should not be backed up.
Should this document be split into two perhaps, one for how Gorilla works and one for how all the other storage systems work? Or can the existing documentation be updated, without making it too.. muddled, perhaps? I am, personally, undecided as to which will make the most pedagogic documentation in the end.