add line numbers for playpen fixes #1593 (#1594)

ErdemOzgen · web-flow · commit 0685f67168e1 · 2022-08-10T13:23:46.000-03:00
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
