docs: add ComponentInHeader import (#2562)

Author: buqiyuan

docs/guide/using-vue.md

@@ -244,6 +244,7 @@ Vitepress currently has SSG support for teleports to body only. For other target
 
 <script setup>
 import ModalDemo from '../components/ModalDemo.vue'
+import ComponentInHeader from '../components/ComponentInHeader.vue'
 </script>
 
 <style>