Update ocamldebug note in CONTRIBUTING.md (#9398)

* update contributing note

* Typo

CONTRIBUTING.md

@@ -53,7 +53,7 @@ Please also bear the following in mind:
 
 ### Using a debugger
 
-To debug the Haxe compiler, you can use either a system debugger (`gdb`/`lldb`), or [ocamldebug](http://caml.inria.fr/pub/docs/manual-ocaml/debugger.html). `ocamldebug` provides a better debugging experience. To use it, compile with `make BYTECODE=1`.
+To debug the Haxe compiler, you can use either a system debugger (`gdb`/`lldb`), or [ocamldebug](http://caml.inria.fr/pub/docs/manual-ocaml/debugger.html). `ocamldebug` provides a better debugging experience. To use it, uncomment `(modes byte)` from [src/dune](src/dune) and recompile.
 
 ### Using printf
 

src/dune

@@ -28,4 +28,6 @@
 	(libraries haxe)
 	(modules haxe)
 	(link_flags (:include ../lib.sexp))
+	; Uncomment to enable bytecode output for ocamldebug support
+	; (modes byte)
 )