docs: fix description loss for using js widgets (#631)

.env.example

@@ -26,3 +26,6 @@ TIDB_SSL=true
 #
 # Notice: this variable will be deprecated in the future.
 EMBEDDING_MAX_TOKENS=2048
+
+# JS Widgets: if you want to use JS widgets, you need to set the following variables to enable CORS.
+# BACKEND_CORS_ORIGINS=['http://localhost:3000', 'https://your-domain.com']

frontend/app/src/pages/docs/javascript.mdx

@@ -2,6 +2,19 @@
 
 What if you could integrate a conversational search window into your website to facilitate instant responses to product-related queries? With the embeddable JavaScript snippet, you can do just that. This feature allows you to copy and embed a simple JavaScript code snippet into your website, typically placed at the bottom right corner of your site.
 
+## Pre-requisites
+
+If you want to embed the JavaScript snippet into your other website, you need to enable it in `.env` file. 
+
+* Step 1: Enable the JavaScript Widget
+
+```bash
+# JS Widgets: if you want to use JS widgets, you need to set the following variables to enable CORS.
+BACKEND_CORS_ORIGINS=['http://localhost:3000', 'https://your-domain.com']
+```
+
+* Step 2: Restart your service
+
 ## How to Embed
 
 To embed the JavaScript snippet, follow these steps: