Tutorial fixes for 8.0.0-alpha

[soniaconnolly]

Make some improvements to the 8.0.0-alpha tutorial after running through it. Each of these items is in a separate commit for ease of reviewing, and also I can revert individual commits if you don't want some of the changes.

• Add catalog_controller.rb comment to ruby snippets to show where to make changes.
• In the facet-fields page, update suggested code for super_special_facet_component.html.erb since the underlying code has changed and the suggested code resulted in an error
• Fix typos in tutorial text
• In the extending-catalog-controller page, update the instructions to fix the static_page_controller routes. The given instructions resulted in an error
• Give a hint about how to show the list of tutorial pages under the Prev/Next buttons. It didn't occur to me to click the menu icon on the upper left, because I had used it to select between versions of the tutorial
• Add the published URL (https://workshop.projectblacklight.org/) to the README so that the repo is more findable