add line numbers for playpen fixes rust-lang#1593

ErdemOzgen · ErdemOzgen · commit a168e9abc9de · 2022-08-01T01:47:14.000+03:00
diff --git a/book.toml b/book.toml
@@ -6,6 +6,7 @@ author = "The Rust Community"
 [output.html.playpen]
 editable = true
 editor = "ace"
+line-numbers = true
 
 [output.html.fold]
 enable = true
