docs: QMK_KEYBOARD_H

Co-authored-by: Ryan <[email protected]>

docs/reference_keymap_extras.md

@@ -9,7 +9,9 @@ Obviously, this can get confusing, so QMK provides language-specific keycode ali
 To select a host keyboard layout, simply `#include` one of the [keycode headers](#header-files) below at the top of your `keymap.c`. Example:
 
 ```c
-#include "keymap_japanese.h"
+#include QMK_KEYBOARD_H
+
+#include "keymap_japanese.h" // [!code focus]
 ```
 
 Alternatively, if using `keymap.json`, add the `host_language` key as shown in the following example. The available languages are those with a _Sendstring LUT Header_ entry in one of the [Header Files](#header-files) tables.