This was written way before the mix-ins sections, made sense back then
but not so much anymore so moving it out.
formatted text and added centering, labels etc while at it.
* Move mix-ins to its own chapter
I don't think it belongs to wheat one which is already packed,
Schwarzbort for once is usually with seeds added.
Once we have more pics it will be even more cramped in the wheat
chapter.
* Fix TeXnicalilities in mix-ins chapter
looooong lines, no use of sinunitx, abbreviations, etc..
* Fix typo
* Update book/book.tex
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Co-authored-by: Hendrik Kleinwaechter <hendrik.kleinwaechter@gmail.com>