message: [book] add option to support absolute URLs
diff: @@ -7,6 +7,7 @@ title = "Mina book"
  [output.html]
  site-url = "/proof-systems/"
  +use-site-url-as-root = true
  curly-quotes = true
  git-repository-url = "https://www.github.com/o1-labs/proof-systems"
  additional-css = ["./assets/css/mdbook-admonish.css"]
  