test 404 redirect.

book.toml

@@ -11,6 +11,7 @@ additional-css = ["theme/pagetoc.css"]
 additional-js  = ["theme/pagetoc.js"]
 git-repository-url = "https://github.com/gnu4cn/rust-lang-zh_CN"
 git-repository-icon = "fa-github"
+input-404 = "not-found.md"
 
 [output.html.print]
 enable = false

src/not-found.md

@@ -0,0 +1,2 @@
+抱歉，此 URL 无效。请使用导航栏或搜索继续。
+<script\>console.log("test embedding javascript in markdown file.");</script\>