Fix usage line in temperature table script

buildroot/share/scripts/createTemperatureLookupMarlin.py

 The main use is for Arduino programs that read data from the circuit board described here:
 http://reprap.org/wiki/Temperature_Sensor_v2.0
 
-Usage: python createTemperatureLookup.py [options]
+Usage: python createTemperatureLookupMarlin.py [options]
 
 Options:
   -h, --help        show this help