[Bug]: Index title is double or nothing

[dellaert]

What happened?

Based on jupyter-books old documentatuion I should include a genindex.md page. But, when I do that, I can't get it to render well in the website:

No title

``{show-index}
``

displays no title only authors, looks ugly

Level 1 title

# Index
``{show-index}
``

displays two titles:

Directive argument

``{show-index} Index
``

also produces two titles :-/

Version

v2.0.0-a0

What Operating System are you using?

Mac OS

Relevant log output

📖 Built genindex.md in 66 ms.
💌 GET  /genindex 200 - - 76.768 ms