add somethign about the NC `database.xml` to the upgrading docs

docs/upgrading.rst

@@ -99,6 +99,17 @@ You can choose from these options:
       # Note: the files are tranferred to a subfolder in the new user's
       # directory
 
+Depending on when you first installed Nextcloud, the ``setup-apps`` job may fail
+during the upgrade. If that happens, execute these commands in order to update
+the failing apps to their newest version, and to remove old files that can cause
+problems.
+
+.. code:: bash
+
+   kubectl exec -n stackspin-apps deployment/nc-nextcloud -- rm -r /var/www/html/custom_apps/onlyoffice
+   kubectl exec -n stackspin-apps deployment/nc-nextcloud -- rm -r /var/www/html/custom_apps/sociallogin
+   flux suspend hr -n stackspin-apps nextcloud && flux resume hr -n stackspin-apps nextcloud
+
 Rocket.Chat
 ~~~~~~~~~~~