Fix K8400 Y min pos, M118 comment

Marlin/src/config/examples/Velleman/K8400/Configuration.h

 
 // Travel limits (mm) after homing, corresponding to endstop positions.
 #define X_MIN_POS 0
-#define Y_MIN_POS 20
+#define Y_MIN_POS 0
 #define Z_MIN_POS 0
 #define X_MAX_POS X_BED_SIZE
 #define Y_MAX_POS Y_BED_SIZE

Marlin/src/gcode/host/M118.cpp

 /**
  * M118: Display a message in the host console.
  *
- *  A1  Append '// ' for an action command, as in OctoPrint
+ *  A1  Prepend '// ' for an action command, as in OctoPrint
  *  E1  Have the host 'echo:' the text
  */
 void GcodeSuite::M118() {