If it's just header links, the subject was brought up a couple days ago; as you can see, the answer hasn't changed much since it was posted in the link sestir provided.
If you're interested in adding static pages, that idea has been brought up a couple times, such as here. I think the general idea is to keep Flarum focused on dynamic content and allow third-party developers to create static page extensions if they desire.
Of course, you could also use the header links extension that's on the roadmap to link to static content on another subdomain, as this site does.
