github action for building and deploying the bookdown guide

[stevencarlislewalker]

• [x] job for creating the html from the rmd in a github action
• [x] deploy the artifact from the job above (https://github.com/marketplace/actions/deploy-to-github-pages)

[stevencarlislewalker]

I think this is complete with https://github.com/canmod/macpan-book/runs/6306859992?check_suite_focus=true, but need to do a little more testing.

At least the site is up with what seems to have been a fully automated deployment.

[stevencarlislewalker]

This is indeed working.

[stevencarlislewalker]

This commit is what finally did it.