fix typo in system docstring

kwant/system.py

@@ -28,7 +28,7 @@ class System(metaclass=abc.ABCMeta):
         the first site in the range, the number of orbitals on each site in the
         range, and the offset of the first orbital of the first site in the
         range.  In addition, the final triple should have the form
-        ``(len(graph.num_nodes), tot_norbs, 0)`` where ``tot_norbs`` is the
+        ``(len(graph.num_nodes), 0, tot_norbs)`` where ``tot_norbs`` is the
         total number of orbitals in the system.
 
     Notes