[Docu] Docu for '{:iteration}' output file name specifier.

Documentation/ProjectFile/prj/time_loop/output/t_prefix.md

@@ -2,7 +2,8 @@ Template for the prefix which will be prepended to the output files. Allowed
 template expressions are:
 - {:meshname}
 - {:timestep}
-- {:time}.
+- {:time}
+- {:iteration}.
 
 Default value: {:meshname}
 

Documentation/ProjectFile/prj/time_loop/output/t_suffix.md

@@ -2,7 +2,8 @@ Template for the suffix which will be appended to the output files. Allowed
 template expressions are:
 - {:meshname}
 - {:timestep}
-- {:time}.
+- {:time}
+- {:iteration}.
 
 Default value: _ts_{:timestep}_t_{:time}