docs: add edge alert

Author: farnabaz

docs/content/4.api/2.composables/1.query-content.md

@@ -202,6 +202,10 @@ const [prev, next] = await queryContent()
 
 Count the number of matched contents based on the query.
 
+::alert
+This feature is available in [edge-channel](https://content.nuxtjs.org/guide/migration/edge-channel) and will be released in next version.
+::
+
 ```ts
 // Count of articles
 const count = await queryContent('articles').count()