Fix header placement in documentation guide.

docs/how-to/add-preparation-and-cleanup-steps-to-backups.md

@@ -59,11 +59,11 @@ variables you can use here:
  * `repositories`: comma-separated paths of all repositories configured in the
    current borgmatic configuration file
 
+## Global hooks
+
 You can also use `before_everything` and `after_everything` hooks to perform
 global setup or cleanup:
 
-## Global hooks
-
 ```yaml
 hooks:
     before_everything: