Elaborate on custom bundle instructions

CUSTOM_BUNDLE.md

@@ -1,13 +1,29 @@
 # Custom bundle
 You can simply make custom bundles yourself, if none of the [distributed packages](https:/plotly/plotly.js/blob/master/dist/README.md) meet your needs, or you want to make a more optimized bundle file with/without specific traces and transforms.
 
-Install plotly.js, move to plotly.js folder then install plotly.js dependencies:
+Clone plotly.js, where the <version> is one of [these](https:/plotly/plotly.js/tags):
+```sh
+git clone --depth 1 --branch <version> https:/plotly/plotly.js.git
+```
+
+Move to plotly.js folder then install plotly.js dependencies:
+```sh
+cd plotly.js
+```
+
+Make sure you have the versions of node/npm that's recommended in the [./CONTRIBUTING.md](./CONTRIBUTING.md#prerequisites) list of Prerequisites
+
+Install the dependencies
 ```sh
-npm i plotly.js
-cd node_modules/plotly.js
 npm i
 ```
 
+Note: You can always switch to another version with:
+```sh
+git fetch
+git checkout <version>
+```
+
 By default all traces and transforms are included in the bundle if you simply run:
 ```sh
 npm run custom-bundle