occ files:scan describe limitations due to session credentials (#520)

* occ files:scan describe limitations due to session credentials

* improve text

modules/administration_manual/pages/configuration/server/occ_command.adoc

@@ -959,6 +959,9 @@ sudo -u www-data php occ files_external:list user_id
 
 TIP: Mounts are only scannable at the point of origin. Scanning of shares including federated shares is not necessary on the receiver side and therefore not possible.
 
+NOTE: Mounts based on session credentials can not be scanned as the users credentials are not available to the occ command set.
+
+
 The `--path`, `--all`, `--groups` and `[user_id]` parameters are exclusive - only one must be specified.
 
 [[the---repair-option]]