Merge pull request #194 from kevanstannard/installation-existing-project

Installation in an existing project documentation

Author: ryyppy

pages/docs/manual/latest/installation.mdx

@@ -34,12 +34,78 @@ Alternatively, **to start a [ReasonReact](https://reasonml.github.io/reason-reac
 
 ## Integrate Into Existing JS Project
 
-You can install the toolchain locally to an existing JS project, through the familiar command:
+You can install ReScript locally into an existing JavaScript project using the following steps.
+
+### Install ReScript
 
 ```sh
 npm install --save-dev bs-platform
 ```
 
-The rest is the same as above. Since we output clean `.bs.js` files, the rest of your existing toolchain (e.g. Babel and Webpack) should mostly just work. Nothing to learn on the bundling side!
+### Create config file
+
+Create a `bsconfig.json` file in the root of your project with the following content.
+
+```json
+{
+  "name": "your-project-name",
+  "bsc-flags": ["-bs-super-errors"],
+  "sources": [
+    {
+      "dir": "src",
+      "subdirs": true
+    }
+  ],
+  "package-specs": [
+    {
+      "module": "es6",
+      "in-source": true
+    }
+  ],
+  "suffix": ".bs.js",
+  "namespace": true,
+  "bs-dependencies": [],
+  "ppx-flags": [],
+  "refmt": 3
+}
+```
+
+> Update `sources` to indicate where your ReScript source files will be located.
+
+See [Build Configuration](build-configuration) for more details on `bsconfig.json`.
+
+### Add scripts to package.json
+
+You may also like to add two scripts to your `package.json` to help with compiling ReScript.
+
+```json
+"scripts": {
+  "re:build": "bsb -make-world -clean-world",
+  "re:watch": "bsb -make-world -clean-world -w"
+}
+```
+
+### Enabling React JS
+
+If you would like to enable React in your ReScript code, use the following additional steps:
+
+Install [Reason React](https://reasonml.github.io/reason-react/en/).
+
+```sh
+npm install reason-react
+```
+
+Make the following changes to your `bsconfig.json` file:
+
+```json
+"reason": { "react-jsx": 3 },
+"bs-dependencies": ["reason-react"],
+```
+
+### Using the compiled code
+
+Since ReScript compiles to clean readable JS files the rest of your existing toolchain (e.g. Babel and Webpack) should just work.
+
+See the [Export to JS guide](import-from-export-to-js#export-to-javascript) to learn how to import ReScript compiled modules into your existing project.
 
-See also our highly recommended guide to [convert from JavaScript](converting-from-js).
+See the [Converting from JS guide](converting-from-js) to learn how to convert existing JS code to ReScript.