GitHub stopped rendering .. contents:: :local: in their UI and instead
opt for expandable table of content that can be shown by clicking
an "index" button at the top-right of the page. It's really nice
when you know it but it's not easily discoverable. Seems that this
is a deliberate choice and there is no going back, so best approach
we can do is to explain it to the users by replacing the index with
explanation where to look for it.

More details here: https://github.com/github/markup/issues/1798