Update M900 verbiage

Marlin/src/gcode/feature/advance/M900.cpp

 #include "../../../module/stepper.h"
 
 /**
- * M900: Set and/or Get advance K factor
+ * M900: Get or Set Linear Advance K-factor
  *
- *  K<factor>                  Set advance K factor
+ *  K<factor>   Set advance K factor
  */
 void GcodeSuite::M900() {
   if (parser.seenval('K')) {

Marlin/src/gcode/gcode.h

  * M867 - Enable/disable or toggle error correction for position encoder modules.
  * M868 - Report or set position encoder module error correction threshold.
  * M869 - Report position encoder module error.
- * M900 - Get and/or Set advance K factor and WH/D ratio. (Requires LIN_ADVANCE)
+ * M900 - Get or Set Linear Advance K-factor. (Requires LIN_ADVANCE)
  * M906 - Set or get motor current in milliamps using axis codes X, Y, Z, E. Report values if no axis codes given. (Requires HAVE_TMC2130)
  * M907 - Set digital trimpot motor current using axis codes. (Requires a board with digital trimpots)
  * M908 - Control digital trimpot directly. (Requires DAC_STEPPER_CURRENT or DIGIPOTSS_PIN)