Update some Data Import documentation

1. Update GitHub documentation for the SRS 999 $i $s being the same for a while, then back to being different (started assigning the same UUIDs in Iris HF3; will stop assigning the same in Lotus)
   • MARC Bibs: same: Iris, Juniper, Kiwi; different: pre-Iris HF3, Lotus+
   • MARC Holdings: same: Kiwi; different: Lotus
   • MARC Authorities: n/a (only SRS records exist in Kiwi; by the time Inventory Authority records exist in Lotus, it will have been changed)
2. Find and update the GitHub 999 documentation (which spans all releases)
3. Once documentation updates are made, add links to this Jira

Notes: It looks like the UUID change was made as part of the work in MODINV-455. There's some helpful discussion at https://github.com/folio-org/mod-inventory/pull/375.