📝 Auto-tune command example (#614)

Author: chepo92

_gcode/M303.md

@@ -56,6 +56,8 @@ examples:
 - pre: 'Auto-tune bed at 60 °C for 8 cycles:'
   code: M303 E-1 C8 S60
 
+- pre: 'Auto-tune hotend at 210 °C for 6 cycles and use the parameters:'
+  code: M303 E0 C6 S210 U1
 ---
 
 This command initiates a process of heating and cooling to determine the proper PID values for the specified hotend or the heated bed.