Fix some config comments

Marlin/src/config/examples/Formbot/T-Rex_2+/Configuration_adv.h

  */
 #define DUAL_X_CARRIAGE
 #if ENABLED(DUAL_X_CARRIAGE)
-  // Configuration for second X-carriage
-  // Note: the first x-carriage is defined as the x-carriage which homes to the minimum endstop;
-  // the second x-carriage always homes to the maximum endstop.
   #define X1_MIN_POS X_MIN_POS        // set minimum to ensure first x-carriage doesn't hit the parked second X-carriage
   #define X1_MAX_POS (X_BED_SIZE)     // set maximum to ensure first x-carriage doesn't hit the parked second X-carriage
   #define X2_MIN_POS 0                // set minimum to ensure second x-carriage doesn't hit the parked first X-carriage

Marlin/src/config/examples/Formbot/T_Rex_3/Configuration.h

 // If the servo can't reach the requested position, increase it.
 #define SERVO_DELAY { 300 }
 
-// Servo deactivation
-//
-// With this option servos are powered only during movement, then turned off to prevent jitter.
+// Only power servos during movement, otherwise leave off to prevent jitter
 //#define DEACTIVATE_SERVOS_AFTER_MOVE
 
 #endif // CONFIGURATION_H

Marlin/src/config/examples/Formbot/T_Rex_3/Configuration_adv.h

   #endif
 #endif
 
-// Enable this for dual x-carriage printers.
-// A dual x-carriage design has the advantage that the inactive extruder can be parked which
-// prevents hot-end ooze contaminating the print. It also reduces the weight of each x-carriage
-// allowing faster printing speeds. Connect your X2 stepper to the first unused E plug.
+/**
+ * Dual X Carriage
+ *
+ * This setup has two X carriages that can move independently, each with its own hotend.
+ * The carriages can be used to print an object with two colors or materials, or in
+ * "duplication mode" it can print two identical or X-mirrored objects simultaneously.
+ * The inactive carriage is parked automatically to prevent oozing.
+ * X1 is the left carriage, X2 the right. They park and home at opposite ends of the X axis.
+ * By default the X2 stepper is assigned to the first unused E plug on the board.
+ */
 #define DUAL_X_CARRIAGE
 #if ENABLED(DUAL_X_CARRIAGE)
-  // Configuration for second X-carriage
-  // Note: the first x-carriage is defined as the x-carriage which homes to the minimum endstop;
-  // the second x-carriage always homes to the maximum endstop.
   #define X1_MIN_POS X_MIN_POS        // set minimum to ensure first x-carriage doesn't hit the parked second X-carriage
   #define X1_MAX_POS (X_BED_SIZE)     // set maximum to ensure first x-carriage doesn't hit the parked second X-carriage
   #define X2_MIN_POS 0                // set minimum to ensure second x-carriage doesn't hit the parked first X-carriage