Add link to git repository for book

JohnTitor · mark-i-m · commit dca6a0755119 · 2019-11-06T22:19:30.000-06:00
diff --git a/book.toml b/book.toml
@@ -7,6 +7,7 @@ description = "A guide to developing rustc"
 create-missing = false
 
 [output.html]
+git-repository-url = "https://github.com/rust-lang/rustc-guide"
 
 [output.html.fold]
 enable = true
