Number chapters starting at 0 so that Instructor Guide is chapter 0?

[braughtg]

From an e-mail:

Hi Grant,
If you'd like to start your Runestone/PreTeXt book at Chapter 0 instead of 1, you need to include the following in your publication files in the publication folder:

 <numbering>
   <divisions chapter-start="0"/>
 </numbering>

Here's my publication file as a sample: https://github.com/bhoffman0/CSAwesome2/blob/main/publication/runestone.xml

best,
-Beryl