Document M155 command

Firmware/Marlin_main.cpp

@@ -3613,6 +3613,7 @@ extern uint8_t st_backlash_y;
 //!@n M129 - EtoP Closed (BariCUDA EtoP = electricity to air pressure transducer by jmil)
 //!@n M140 - Set bed target temp
 //!@n M150 - Set BlinkM Color Output R: Red<0-255> U(!): Green<0-255> B: Blue<0-255> over i2c, G for green does not work.
+//!@n M155 - Automatically send temperatures
 //!@n M190 - Sxxx Wait for bed current temp to reach target temp. Waits only when heating
 //!          Rxxx Wait for bed current temp to reach target temp. Waits when heating and cooling
 //!@n M200 D<millimeters>- set filament diameter and set E axis units to cubic millimeters (use S0 to set back to millimeters).
@@ -6406,6 +6407,17 @@ Sigma_Exit:
     }
 
 #ifdef AUTO_REPORT_TEMPERATURES
+    /*!
+	### M155 - Automatically send temperatures <a href="https://reprap.org/wiki/G-code#M155:_Automatically_send_temperatures">M155: Automatically send temperatures</a>
+	#### Usage
+	
+		M155 [ S ]
+	
+	#### Parameters
+	
+	- `S` - Set temperature autoreporting interval in seconds. 0 to disable. Maximum: 255
+	
+    */
     case 155:
     {
         if (code_seen('S'))