Add note on system IDs to docs

diff --git a/docs/tans.rst b/docs/tans.rst
index cdb5de88823fae717c5aefccb2af2b82de5cafa7..f3a3eedd0d5913a46b001d2caa06714c8cf88fd3 100644 (file)
--- a/docs/tans.rst
+++ b/docs/tans.rst
@@ -154,6 +154,13 @@ You SHOULD use this facility together with the client and dialog state restorati
     print(response.status)
     print(response.responses)
 
+System IDs
+----------
+
+During your first connection, the bank will assign your client application a "system ID" accessible
+as ``client.system_id``. Some banks require you to pass the same system ID with your next connection
+with ``FinTS3PinTanClient(..., system_id=stored_system_id)`` to avoid a TAN requirement on every login.
+(This happens automatically when using ``from_data``).
 
 Reference
 ---------