Use this shortcode to add an inline related articles block to your Instant Articles.
[wpna_related_articles title="My Optional Title" ids="1343,1388,1989"]<br>
Place this shortcode in your WordPress post and in the Instant Version a related articles block will appear. IDs should be a comma separate list of the WordPress post ids you wish to link to. The title param is optional. Nothing will appear in the actual post that's shown on your site.
You can read more about the related articles in the official Facebook Documentation.