📜 Add directions on where to save custom js. (#270)

advanced/custom/js.mdx

@@ -9,9 +9,9 @@ description: 'Add JavaScript functionality globally'
 
 Custom JS allows you to add custom executable code globally. It is the equivalent of adding a `<script>` tag with JS code into every page.
 
-## Adding script.js
+## Adding Custom JavaScript
 
-For example, you can add the following `script.js` file to enable [Google Analytics](https://marketingplatform.google.com/about/analytics) across the entire documentation.
+Any `.js` file inside the content directory of your docs will be included in every documentation page. For example, you can add the following `ga.js` file to enable [Google Analytics](https://marketingplatform.google.com/about/analytics) across the entire documentation.
 
 ```js
 window.dataLayer = window.dataLayer || [];