How does one add a Sitemap to a site that is using the new Homestead responsive platform?

In the old site builder, I could add files via the file manager.  I can't seem to find that anywhere I look on the new HS platform.  Adding the Sitemap is easy, I just need to know where to do it on the new platform.

I looked through a bunch of questions here, but all the answers seem to apply to the old Site Builder.