Feature request: TOC (Table Of Contents) on the right side

## Feature request

#### What problem does this feature solve?
Include a TOC (Table of Contents) section on the right side.

#### What does the proposed API look like?
-

#### How should this be implemented in your opinion?
The Table of contents should be autogenerated and triggered with a flag, similar to how the navigation or sidebars work. It would contain a separate file toc.md for example that would be used for styling and supplemental configuration.

It would look and work similar to how it's implemented currently for the android documentation:
https://developer.android.com/games/develop/overview

#### Are you willing to work on this yourself?
No