Mention units for MANUAL_FEEDRATE (#18993)

Marlin/Configuration_adv.h

@@ -1025,7 +1025,7 @@
 // @section lcd
 
 #if EITHER(ULTIPANEL, EXTENSIBLE_UI)
-  #define MANUAL_FEEDRATE { 50*60, 50*60, 4*60, 2*60 } // Feedrates for manual moves along X, Y, Z, E from panel
+  #define MANUAL_FEEDRATE { 50*60, 50*60, 4*60, 2*60 } // (mm/m) Feedrates for manual moves along X, Y, Z, E from panel
   #define SHORT_MANUAL_Z_MOVE 0.025 // (mm) Smallest manual Z move (< 0.1mm)
   #if ENABLED(ULTIPANEL)
     #define MANUAL_E_MOVES_RELATIVE // Display extruder move distance rather than "position"