Update JSOO and adapt contributing docs (#7218)

Author: cknitt

CONTRIBUTING.md

@@ -214,13 +214,7 @@ This is usually the file you want to create to test certain compile behavior wit
 
 The "Playground bundle" is a JS version of the ReScript compiler; including all necessary dependency files (stdlib / belt etc). It is useful for building tools where you want to compile and execute arbitrary ReScript code in the browser.
 
-The ReScript source code is compiled with a tool called [JSOO (js_of_ocaml)](https://ocsigen.org/js_of_ocaml/4.0.0/manual/overview), which uses OCaml bytecode to compile to JavaScript and is part of the bigger OCaml ecosystem.
-
-Install `jsoo` via `opam`:
-
-```sh
-opam install js_of_ocaml.4.0.0
-```
+The ReScript source code is compiled with a tool called [JSOO (js_of_ocaml)](https://ocsigen.org/js_of_ocaml/latest/manual/overview), which uses OCaml bytecode to compile to JavaScript and is part of the bigger OCaml ecosystem.
 
 ### Building the Bundle
 

dune-project

@@ -35,7 +35,7 @@
   (cppo
    (= 1.6.9))
   (js_of_ocaml
-   (= 5.8.1))
+   (= 5.9.1))
   (ounit2
    (= 2.2.7))
   (reanalyze

rescript.opam

@@ -12,7 +12,7 @@ depends: [
   "yojson" {with-test & = "2.2.2"}
   "ocaml-lsp-server" {with-dev-setup & = "1.19.0"}
   "cppo" {= "1.6.9"}
-  "js_of_ocaml" {= "5.8.1"}
+  "js_of_ocaml" {= "5.9.1"}
   "ounit2" {= "2.2.7"}
   "reanalyze" {= "2.25.1"}
   "dune"