TOC is broken in documentation

[XzzX]

https://pyiron-workflow.readthedocs.io/en/latest/source/examples.html

There should only be three notebooks and captions underneath.

[liamhuber]

Good catch. At somepoint I added # Subsections to the quickstart as markdown cells instead of ## Subsections, so the parser is (sensibly) putting them at the top level of the ToC. I've got a local branch that should fix it, but I need to find 10 minutes to go and renew my GPG key before pushing. I might not fix it "soon", but it will be the next code thing I do.

[liamhuber]

Fixed in #511