fixed the start_print sequence overrides

The template was missing the macro header and 'gcode:' line
to be able to work correctly

user_templates/overrides.cfg

@@ -24,11 +24,13 @@
 #-------------------------#
 
 ## The START_PRINT sequence is modular and fully customizable. A default START_PRINT sequence is auto-populated based on
-## your probe choice (TAP, Dockable, Inductive), but if for some reasons you still want to modify it, please uncomment the
-## following `variable_startprint_actions` definition. You can use any number of action or even duplicate some actions if needed.
+## your probe choice (TAP, Dockable, Inductive), but if for some reasons you still want to modify it, please uncomment the following 3
+## lines to define a new `variable_startprint_actions`. You can use any number of action or even duplicate some actions if needed.
 ## Available actions: "bed_soak", "chamber_soak", "extruder_heating", "tilt_calib", "z_offset", "bedmesh", "purge", "clean", "primeline"
 ##
+# [gcode_macro _USER_VARIABLES]
 # variable_startprint_actions: "action1", "action2", ...
+# gcode: # do not remove this line
 
 
 #-------------------------#