added proper management of the vibration test accels

docs/macros/vibrations_tuning.md

@@ -17,6 +17,7 @@ Call the `VIBRATIONS_CALIBRATION` macro with the direction and speed range you w
 |DIRECTION|"XY"|direction vector where you want to do the measurements. Can be set to either "XY", "AB", "ABXY", "A", "B", "X", "Y", "Z", "E"|
 |Z_HEIGHT|20|z height to put the toolhead before starting the movements. Be careful, if your ADXL is under the nozzle, increase it to avoid a crash of the ADXL on the bed of the machine|
 |VERBOSE|1|Wether to log the current speed in the console|
+|ACCEL|3000 (or max printer accel)|accel in mm/s^2 used for all the moves. Try to keep it relatively low to avoid bad oscillations that affect the measurements, but but high enough to reach constant speed for >~70% of the segments|
 |MIN_SPEED|20|minimum speed of the toolhead in mm/s for the movements|
 |MAX_SPEED|200|maximum speed of the toolhead in mm/s for the movements|
 |SPEED_INCREMENT|2|speed increments of the toolhead in mm/s between every movements|