add documentation for log file directory

Author: glesur

doc/source/reference/idefix.ini.rst

@@ -411,6 +411,9 @@ This section describes the outputs *Idefix* produces. For more details about eac
 +================+=========================+==================================================================================================+
 | log            | integer                 | | Time interval between log outputs, in code steps (default 100).                                |
 +----------------+-------------------------+--------------------------------------------------------------------------------------------------+
+| log_dir        | string                  | | directory for log file outputs. Default to "./"                                                |
+|                |                         | | The directory is automatically created if it does not exist.                                   |
++----------------+-------------------------+--------------------------------------------------------------------------------------------------+
 | dmp            | float, float+char       | | 1st parameter: Code time interval between dump outputs, in code units.                         |
 |                |                         | | If negative, the first parameter is ignored.                                                   |
 |                |                         | | 2nd parameter (optional): Wallclock time interval between two dumps. The ending character      |