Add help argument to usage menu

Change-Id: I948519f7f2c4bb148e552e2b9662bd443a53faca
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/argument.C b/argument.C
index 15c258e..e9a9088 100644
--- a/argument.C
+++ b/argument.C
@@ -40,6 +40,7 @@
 {
     std::cerr << "Usage: " << argv[0] << " [options]" << std::endl;
     std::cerr << "Options:" << std::endl;
+    std::cerr << "    --help               print this menu" << std::endl;
     std::cerr << "    --path=<path>        sysfs location to monitor"
               << std::endl;
 }