Improve help message

Author: erlingrj

core/reactor_common.c

@@ -889,7 +889,7 @@ void usage(int argc, const char* argv[]) {
   printf("   The logical start time of the program, expressed as a duration since the epoch of the underlying system "
          "clock.\n");
   printf("   The units are nsec, usec, msec, sec, minute, hour, day, week or the plurals of those.\n");
-  printf("   On linux, to compute a start time in 2 minutes you can do:.\n");
+  printf("   On linux, to compute a start time of 2 minutes into the future, expressed in seconds you can do:.\n");
   printf("     `date -d \"2 minutes\" +%%s`.\n\n");
 #ifdef FEDERATED
   printf("  -r, --rti <n>\n");