add help

main.cpp

@@ -29,8 +29,12 @@ int main(int argc, char **argv)
     int tcount = 0;
     int maxiter = 0;
 
-    while ((c = getopt(argc, argv, "t:i:")) != -1) {
+    while ((c = getopt(argc, argv, "ht:i:")) != -1) {
         switch (c) {
+            case 'h':
+                std::cout << "Usage: " << argv[0] << " [-t] [thread count] " <<
+                    "[-i] [max iterations]" << std::endl;
+                exit(0);
             case 't':
                 targ = optarg;
                 break;