Update part-5-async-logic.md (#4617)

Highlight next line as {renderedPosts} in example changes to {content} for the reader following along.

Author: kalyncoose

docs/tutorials/essentials/part-5-async-logic.md

@@ -592,6 +592,7 @@ export const PostsList = () => {
   return (
     <section className="posts-list">
       <h2>Posts</h2>
+      // highlight-next-line
       {content}
     </section>
   )