📝 Update MPCTEMP G-Code M306 T (#24535)

M306 simply reports current values. M306 T starts autotune process.

Marlin/Configuration.h

@@ -653,7 +653,7 @@
  *
  * Use a physical model of the hotend to control temperature. When configured correctly
  * this gives better responsiveness and stability than PID and it also removes the need
- * for PID_EXTRUSION_SCALING and PID_FAN_SCALING. Use M306 to autotune the model.
+ * for PID_EXTRUSION_SCALING and PID_FAN_SCALING. Use M306 T to autotune the model.
  */
 #if ENABLED(MPCTEMP)
   //#define MPC_EDIT_MENU                             // Add MPC editing to the "Advanced Settings" menu. (~1300 bytes of flash)