Add alt text to a single chapter

[geealbers]

Find the next chapter in the book that does not yet have alt text, and write and add the text to the figures.yaml file, on a new branch. You can use the print book or the online site to see the figures, or you can preview the book on your machine with quire preview. Note that when you clone a Quire repository from GitHub, you'll need to first run npm install before any quire commands will work.

cd conserving-canvas
npm install
quire preview

When your branch is ready, submit the texts as a Pull Request, and tag me as Reviewer.