Create class transcribe guide page with keyboard navigation information

It's pretty great we have information over many buttons and follow a good set of web conventions so setting up information would not be too hard. Every site seems to have their own non-standard conventions so having this can help users. For example when going "Back" in the site we can use `Alt`+`Left Arrow` but not `Backspace` or `Control`+`[`.

The issue names no file or test; start by locating existing guide or information pages in the React + Redux frontend and follow their page structure. Add a ClassTranscribe guide page covering the site's keyboard navigation conventions, including the stated Back shortcut example, and verify that the page is reachable and readable.

Written by the indexing model from the issue text.