Headings' order in dataset docs are incorrect

[nesnoj]

See 2. in #92 (review)

[dvdstrzl]

I added the "#" intentionally, because:

"The TOC is not intended to list h1 elements. In HTML5 only one h1 is valid per page or article tag and the whole content is enclosed in an article tag, so adding multiple h1 is not considered valid. Only 2nd+ level items are listed. This is intended behavior. Also see squidfunk/mkdocs-material#654."
(squidfunk/mkdocs-material#818 (comment))

We could add a "#" via the script to every heading.

[dvdstrzl]

That should do the trick (?)