message: Add const keyword to book highlighting
diff: @@ -2,7 +2,7 @@ import hljs from "highlight.js/lib/core";
  hljs.registerLanguage("fathom", (hljs) => {
  const KEYWORDS = {
  - keyword: "else enum Format if Kind match repr struct Type",
  + keyword: "const else enum Format if Kind match repr struct Type",
  built_in: [
  "Int F32 F64 Bool true false Array",
  "U8 U16Le U16Be U32Le U32Be U64Le U64Be",
  