Add submenus for the guides in each guide section

[morskyjezek]

I'd like to suggest adding a submenu that lists all of the guides in each of the guide section. This is currently the case in the Additional Resources menu, where Tools opens an "Overview" submenu. But in the Guides section, the various guides don't appear in the menus at the left.

I notice some of the links are external links, but many are internal to other pages in the documentation.