Update CONTRIBUTING with correct playground cmi / cmj information

CONTRIBUTING.md

@@ -307,11 +307,9 @@ A `.cmi` file is an [OCaml originated file extension](https://waleedkhan.name/bl
 
 In this repo, these files usually sit right next to each compiled `.ml` / `.res` file. The structure of a `.cmj` file is defined in [js_cmj_format.ml](jscomp/core/js_cmj_format.ml). You can run a tool called `./jscomp/bin/cmjdump.exe [some-file.cmj]` to inspect the contents of given `.cmj` file.
 
-`.cmj` files are required to compile modules (this includes modules like RescriptReact). ReScript includes a subset of modules by default, which can be found in `jscomp/stdlib-406` and `jscomp/others`. You can also find those modules listed in the `jsoo` call in `scripts/repl.js`. As you probably noticed, the generated `playground` files are all plain `.js`, so how are the `cmj` / `cmi` files embedded?
+`.cmj` files are required to compile modules (this includes modules like RescriptReact). ReScript includes a subset of modules by default, which can be found in `jscomp/stdlib-406` and `jscomp/others`. You can also find those modules listed in the JSOO call in `scripts/repl.js`. As you probably noticed, the generated `playground` files are all plain `.js`, so how are the `cmj` / `cmi` files embedded?
 
-`repl.js` calls an executable called `cmjbrowser.exe` on every build, which is a compile artifact from `jscomp/main/jscmj_main.ml`. It is used to serialize `cmj` / `cmi` artifacts into two files called `jscomp/core/js_cmj_datasets.ml`. These files are only linked for the browser target, where ReScript doesn't have access to the filesystem. When working on ReScript, you'll see diffs on those files whenever there are changes on core modules, e.g. stdlib modules or when the ocaml version was changed. We usually check in these files to keep it in sync with the most recent compiler implementation. JSOO will pick up those files to encode them into the `compiler.js` bundle.
-
-For any other dependency needed in the playground, such as `RescriptReact`, you will be required to serialize your `.cmi` / `.cmt` files accordingly from binary to hex encoded strings so that ReScript Playground's `ocaml.load` function can load the data. We use `jsoo`'s builtin functionality to create `cmij.js` files for that. Check out `packages/playground-bundling/scripts/generate_cmijs.js` for details.
+JSOO offers an `build-fs` subcommand that takes a list of `.cmi` and `.cmj` files and creates a `cmij.js` file that can be loaded by the JS runtime **after** the `compiler.js` bundle has been loaded (either via a `require()` call in Node, or via `<link/>` directive in an HTML file). Since we are shipping our playground with third party modules like `RescriptReact`, we created a utility directory `packages/playground-bundling` that comes with a utility script to do the `cmij.js` file creation for us. Check out `packages/playground-bundling/scripts/generate_cmijs.js` for details.
 
 ### Publishing the Playground Bundle on our KeyCDN