globals: Use _KM_OPTIONS for end-user startup gcode

Allows end-user startup customization by running _KM_OPTIONS gcode
at startup, immediately after our macros initialize.

README.md

@@ -78,7 +78,12 @@ overridden by creating a corresponding variable with a new value in your
 #  {'name' : 'PLA',  'extruder' : 200.0, 'bed' : 60.0},
 #  {'name' : 'PETG', 'extruder' : 230.0, 'bed' : 85.0},
 #  {'name' : 'ABS',  'extruder' : 245.0, 'bed' : 110.0, 'chamber' : 60}]
-gcode: # This line required by Klipper.
+gcode: 
+# Any code you put here will run at klipper startup, after the initialization
+# for these macros. For example, you could uncomment the following line to
+# automatically adjust your bed surface offsets to account for any changes made
+# to your Z endstop or probe offset.
+#   ADJUST_SURFACE_OFFSETS
 
 # This line includes all the standard macros.
 [include klipper-macros/*.cfg]

globals.cfg

@@ -151,6 +151,8 @@ gcode:
   # This needs to be its own macro so it gets evaluated after _KM_GLOBALS runs.
   _CHECK_GLOBALS
   _INIT_SURFACES
+  # This is any end-user gcode that need to run after macro initialization.
+  _KM_OPTIONS
 
 [gcode_macro _check_globals]
 description: Checks global variables and stops printer on an invalid value.