Link assets guide into the book for setting up dependencies

[willtcarey]

https://github.com/brandnewbox/devops/blob/main/best-practices/assets.md

[hannahekehoe]

Adding a bit more detail to this issue: The problem first appears when adding Stimulus, and then becomes an issue again when adding in Bootstrap. I think that an explanation of the asset pipeline and a guide for set up in the Stimulus section would make sense and perhaps fix the issue since the later Bootstrap chapter references webpack files that are not set up by the time you get there (ie. there is no config/webpack/environment.js in the file explorer yet it is referenced for modification). The chapter also asks you to add import statements to app/javascript/packs/application.js yet there is no packs subfolder of app/javascript by the time you reach this step.