Add note about base_dir functions requiring LV_USE_BIDI

src/lv_core/lv_obj.c

@@ -1657,7 +1657,8 @@ void lv_obj_set_parent_event(lv_obj_t * obj, bool en)
 }
 
 /**
- * Set the base direction of the object
+ * Set the base direction of the object.
+ * @note This only works if LV_USE_BIDI is enabled.
  * @param obj pointer to an object
  * @param dir the new base direction. `LV_BIDI_DIR_LTR/RTL/AUTO/INHERIT`
  */