added --file option to documentatioin

README.md

@@ -32,6 +32,10 @@ variables to change it's behaviour.
 
 The parameters are:
 
+- **-f \<file\>, --file \<file\>**: Allows to specify which configuration file
+to load manually. Tha option can be repeated to allows the loading of multiple
+configuration file, the last overloading the previously defined ones in case of
+identical variable name.
 - **-m \<list\>, --module \<list\>**: Allows to manually give a module list and
 overide the *MODULE_LIST* variable declaration. The list is a comma separated
 module name. If that option is provided, the module list is mandatory.