Added detail on backup compression flag (#1808)

This support case shows how a customer is misled by absolute description
of backup being faster when compression is disabled.


https://trello.com/c/xsCLZrwy/7747-s3dbs-risk-management5181-backup-is-taking-more-time-with-compressfalse

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Co-authored-by: Reneta Popova <[email protected]>

Author: tonbut

modules/ROOT/pages/backup-restore/online-backup.adoc

@@ -121,8 +121,7 @@ If <database> is "*", `neo4j-admin` will attempt to back up all databases of the
 |
 
 |--compress[=true\|false]
-|Request backup artifact to be compressed. If disabled, backup artifact creation is faster but
-the size of the produced artifact will be approximately equal to the size of backed-up database.
+|Request backup artifact to be compressed. Compression can yield a backup artefact many times smaller, but the exact reduction depends upon many factors, including the database format and the kind of data stored. If disabled, the size of the produced artifact will be approximately equal to the size of the backed-up database. The speed of the backup operation is affected by compression, but which is faster depends upon the relative performance of CPU and storage. If backup speed is important, consider evaluating both options - with compression enabled and disabled.
 |true
 
 | --expand-commands