add instructions for how to create a static backup
This should be done before Q4 starts in case Ruud needs it
specific use case is when the website is down and if you need to share the book with people. Make a short set of instructions and perhaps also video about:
- build book locally
- find _build folder
- zip it
- send it
- show how to access the "website" via the browser URL
- optionally include and example for setting up a python server and finding the IP (mention that interactive features can then be enabled/tested)