Update commands list for M100 parameter

thanks @limited660

src/ArduinoDUE/Repetier/Repetier.ino

@@ -90,7 +90,7 @@ Custom M Codes
 - M85  - Set inactivity shutdown timer with parameter S<seconds>. To disable set zero (default)
 - M92  - Set axisStepsPerMM - same syntax as G1
 - M99 S<delayInSec> X0 Y0 Z0 - Disable motors for S seconds (default 10) for given axis.
-- M100 clean nozzle
+- M100 T<extruderNum> clean nozzle, no extruder specified clean all available
 - M104 S<temp> T<extruder> P1 F1 - Set temperature without wait. P1 = wait for moves to finish, F1 = beep when temp. reached first time
 - M105 X0 - Get temperatures. If X0 is added, the raw analog values are also written.
 - M112 - Emergency kill