Support for TOC in README files

It seems this was something which was supported in the past, but with recent migrations to a different markdown rendering engine it is not anymore. So I am opening an issue to point to this again.

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Updated description with a now working example

• Supporting Table of Contents
  • Syntax
    • Other options
  • How do we know it is done?

Supporting Table of Contents

Does this seem like something we should support? And allow in issue descriptions?

Syntax

Let use the [[_TOC_]] syntax for now

Other options

If CommonMark ever officially supports something, we'll add that

How do we know it is done?

When an auto-generated table of contents appears above ✅