Our current sitemap.xml covers the most basic case. Although, there are users with other needs that require a more customized sitemap.xml.

We should implement the same mechanism that we do for custom 404.html, where we provide the most basic one (Maze found) with the ability to change it by adding your own 404.html to the output generated by Sphinx.

So, we could check first for `sitema

The example book created by jupyter-book create creates files with permissions 775. None of these files are really executable, and therefore the correct permissions should be 664 (or probably 644)

To Reproduce

jupyter-book create test; ls -al test

The Windows screenshots in the introductory section look dated, because they were made with Windows 7, and Panda3D 1.8. We should redo them on Windows 10.