config: add a help message for people that confuse Klipper with KlipperScreen

ks_includes/config.py

@@ -196,6 +196,13 @@ class KlipperScreenConfig:
             for key in config[section]:
                 if key not in bools and key not in strs and key not in numbers:
                     msg = f'Option "{key}" not recognized for section "[{section}]"'
+                    if key == "gcode" and section.startswith("menu"):
+                        msg = (
+                            msg + "\n\n"
+                            + "The 'gcode' option is not part of KlipperScreen syntax\n"
+                            + "it's meant for text/graphical LCDs (usually blue) controlled by Klipper itself\n"
+                            + "please consult KlipperScreen documentation."
+                        )
                     if key == "camera_url":
                         msg = (
                             "camera_url has been deprecated in favor of moonraker cameras\n\n"