Explicit that one can provide several files to the -i option

doc/doxygen/chapters/380_offline_performance_tools.doxy

@@ -129,7 +129,7 @@ collect the trace files from the MPI nodes, and
 specify them all on the command <c>starpu_fxt_tool</c>, for instance:
 
 \verbatim
-$ starpu_fxt_tool -i /tmp/prof_file_something1 -i /tmp/prof_file_something2
+$ starpu_fxt_tool -i /tmp/prof_file_something*
 \endverbatim
 
 By default, all tasks are displayed using a green color. To display tasks with

tools/starpu_fxt_tool.c

@@ -30,8 +30,9 @@ static void usage()
 	fprintf(stderr, "Usage: %s [ options ]\n", PROGNAME);
         fprintf(stderr, "\n");
         fprintf(stderr, "Options:\n");
-	fprintf(stderr, "   -i <input file>     specify the input file. This can be specified several\n");
-	fprintf(stderr, "                       times for MPI execution case\n");
+	fprintf(stderr, "   -i <input file[s]>  specify the input file[s]. Several files can be provided,\n");
+	fprintf(stderr, "                       or the option specified several times for MPI execution\n");
+	fprintf(stderr, "                       case\n");
         fprintf(stderr, "   -o <output file>    specify the output file\n");
         fprintf(stderr, "   -c                  use a different colour for every type of task\n");
 	fprintf(stderr, "   -no-events          do not show events\n");