docs: add warning badge

Author: sxzz

docs/macros/index.md

@@ -8,7 +8,7 @@ Please make sure `unplugin-vue-macros` is set up correctly. If you haven't yet,
 - [defineModel](/macros/define-model)
 - [defineProps](/macros/define-props)
 - [definePropsRefs](/macros/define-props-refs)<WarnBadge>unstable</WarnBadge>
-- [defineSlots](/macros/define-slots)
+- [defineSlots](/macros/define-slots)<WarnBadge>unstable</WarnBadge>
 - [defineRender](/macros/define-render)
 - [shortEmits](/macros/short-emits)
 - [shortVmodel](/macros/short-vmodel)