docs: Add help center link to delete conversation endpoint (#397)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: marcmlc

descriptions/0/api.intercom.io.yaml

@@ -6900,6 +6900,8 @@ paths:
         {% admonition type="info" name="Required scope for retain_metrics=false" %}
         Using `retain_metrics=false` requires the `delete_conversations_and_metrics` OAuth scope.
         {% /admonition %}
+
+        For more info, see [this help center article](https://www.intercom.com/help/en/articles/13885146-deleting-a-conversation).
       responses:
         '200':
           description: successful