IOSS: Clarify select_step documentation

Author: gsjaardema

packages/seacas/libraries/ioss/src/main/shell_interface.C

@@ -286,8 +286,8 @@ void IOShell::Interface::enroll_options()
                   nullptr);
 
   options_.enroll("select_steps", Ioss::GetLongOption::OptType::MandatoryValue,
-                  "comma-separated list of steps that should be transferred to output database\n"
-                  "\t\tEnter a negative value to count from end. -1 is last, -2 is second last.",
+                  "comma-separated 1-based list of steps that should be transferred to output database\n"
+		  "\t\tEnter a negative value to count from end. -1 is last, -2 is second last.",
                   nullptr);
 
   options_.enroll("append_after_time", Ioss::GetLongOption::OptType::MandatoryValue,