Update the stator-rotor calibration with the default value (#335)

Co-authored-by: Jacopo <[email protected]>

docs/icub_robot_calibration/icub3-stator-rotor-autocalibration.md

@@ -41,6 +41,8 @@ Once `yarprobotinterface` is running, check the log messages and look for a `DEB
 
 Looking at par64, the rightmost 4 digits are the offset: `0x0079` = `121` degrees; this is the value to save in the file (see next steps). 
 
+The first `DEBUG` messages have the rightmost 4 digits equal to the default value `0xffff` until the offset is not found. 
+
 !!!warning
     The 8 leftmost digits (in the example `0xffcc0042`) must be not `0`!<br>
     Otherwise the calibration is failed/not completed.