Add additional documentation for LaTeX PDFs

[Songtech-0912]

This adds additional information regarding the table of contents structure of LaTeX PDF exports, fixing unexpected behavior where LaTeX pdfs show section numbers as "0.X.Y" in the table of contents. For more information, see myst-templates/plain_latex_book#4, where this PR came from.

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[schmoelder]

Very nice to see that this is being addressed. Thanks a lot!

For reference, these two issues seem to be related:

• Numbering of headers and titles doesn't work as expected #2002
• files included as sections rather than chapters in LaTeX book template. #2042

[cycomachead]

Thank you! This is very helpful for a book project I am working on!

Just musing... It would be great if we could find a way to them keep the regular toc and the PDF export ones in sync, but I've moved all this config to separate yaml files:

extends:
  - toc.yml
  - toc_pdf.yml
  - toc_pdf_alternates.yml

This will at least make diff'ing the list of files a little easier over time. :)

[agoose77]

Thank you! This is very helpful for a book project I am working on!

Just musing... It would be great if we could find a way to them keep the regular toc and the PDF export ones in sync, but I've moved all this config to separate yaml files:

extends:
  - toc.yml
  - toc_pdf.yml
  - toc_pdf_alternates.yml

This will at least make diff'ing the list of files a little easier over time. :)

I agree with this point — we would like to give this some design thought!