added security notice following JS guidelines on env variables

Author: juliamuiruri4

articles/ai-services/agents/includes/quickstart-javascript.md

@@ -69,6 +69,12 @@ For example, your connection string may look something like:
 
 Set this connection string as an environment variable named `PROJECT_CONNECTION_STRING` in a `.env` file.
 
+### Security Notice 
+
+> **Important**: This quickstart code uses environment variables for sensitive configuration. Never commit your `.env` file to version control by making sure `.env` is listed in your `.gitignore` file.
+> _Remember: If you accidentally commit sensitive information, consider those credentials compromised and rotate them immediately._
+
+
 Next, create an `index.js` file and paste in the code below:
 
 ```javascript