📜 Add directions on where to save custom js.

Author: mxbaylee

advanced/custom/js.mdx

@@ -11,6 +11,8 @@ Custom JS allows you to add custom executable code globally. It is the equivalen
 
 ## Adding script.js
 
+To add custom JavaScript functionality globally, you need to create a `script.js` file at the root of your project. In case of a monorepo, this file should be at the same level as your `mint.json` file.
+
 For example, you can add the following `script.js` file to enable [Google Analytics](https://marketingplatform.google.com/about/analytics) across the entire documentation.
 
 ```js