These docs outline some of the custom includes that are provided by the theme and can be modified by the user.

Co-authored-by: Matt Wang <matt@matthewwang.me>
Co-authored-by: Patrick Marsceill <pmarsceill@users.noreply.github.com>

(cherry picked from commit dffb2706a158784e2f3091f895a868e373683bc8)

This commit makes the dark mode preview feel a little more interactive
and it also pulls some duplicated code into one file so that people like
me aren't stumped when they are looking at the wrong page!

For pages in utilities/, reorder `nav_order` to follow `parent`.