Updated dcdbquery usage instructions for sensor operations.

tools/dcdbquery/dcdbquery.cpp

@@ -54,7 +54,9 @@ void usage(void)
             << "When the -r option is specified, timestamps will be reported in internal (raw)" << std::endl
             << "format (nanoseconds since epoch) insted of ISO human readable form." << std::endl
             << "When the -l option is specified, times for <Start>, <End>, and in the generated" << std::endl
-            << "output will be interpreted / printed in the local time zone." << std::endl;
+            << "output will be interpreted / printed in the local time zone." << std::endl
+            << "To print out sensor operations, type <operation>(<Sensor>), e.g., derivative(sensor name)." << std::endl
+            << "Currently available options for the <operation> field are: delta, derivative, integral." << std::endl;
   }
   else {
       std::cout << "Invalid request." << std::endl;