[Documentation / Link] The link to the sinatra book appears to no longer be available

I was looking at https://sinatrarb.com/documentation.html to see whether I can refresh my knowledge about sinatra with new content.

As I clicked on the links there, I came to the one named "The Sinatra Book".

As I clicked on it, I was redirected to:

https://sinatra-org-book.herokuapp.com/

And this said "nothing to see there". So no Sinatra book.

I think the main link to the book should be removed from:

https://sinatrarb.com/documentation.html

For now.

However had, if anyone has contact to the authors, it may be useful to host the book here at the github repository; or as a separate entry, in the sinatra project.

And if the authors are available and have not specified, perhaps also we could all help maintain the information in it (once it is hosted here on github). Having a sinatra book would be really nice as an intro-point to learning sinatra. I think Konstantin wrote one book many years ago, and this is still useful, but so many things seem to have changed over the years and it is not trivial to find out what all has changed and what has not - the available documentation is a bit dispersed right now.

Anyway this is the concern I wanted to mention here. Cheers!