Document how to build the site locally

[funnelfiasco]

But first, figure out how to. :-)

         > Hey @funnelfiasco, how are you testing this locally? I installed jekyll, but haven't found the right combination of commands to build and run the site

I'm not. I haven't found the right combination of commands either, so I force push to the main branch of my fork, which runs the build pipeline. When I'm happy with how it looks, I squash those commits into one and open a PR.

Originally posted by @funnelfiasco in #183 (comment)