add a fancy octocat button

adsick · adsick · commit e5965a43b952 · 2021-11-19T23:50:48.000+02:00
diff --git a/book.toml b/book.toml
@@ -9,3 +9,6 @@ editor = "ace"
 
 [output.html.fold]
 enable = true
+
+[output.html]
+git-repository-url = "https://github.com/rust-lang/rust-by-example"
