Fix docs about the relative speeds of different checks (#945).

Reviewed-on: https://projects.torsion.org/borgmatic-collective/borgmatic/pulls/945

docs/how-to/deal-with-very-large-backups.md

@@ -89,8 +89,9 @@ checks:
 
 Here are the available checks from fastest to slowest:
 
- * `repository`: Checks the consistency of the repository itself.
- * `archives`: Checks all of the archives in the repository.
+ * `archives`: Checks all of the archives metadata in the repository.
+ * `repository`: Checks the consistency of the whole repository. The checks run
+   on the server and do not cause significant network traffic.
  * `extract`: Performs an extraction dry-run of the latest archive.
  * `data`: Verifies the data integrity of all archives contents, decrypting and decompressing all data.
  * `spot`: Compares file counts and contents between your source files and the latest archive.