Add CORS and Bundling sections to README-TEMPLATE (Azure#13516)

## What

- Add a section on setting up CORS and creating a browser bundle to our template readme.

## Why

CORS is one of the first roadblocks a user will encounter when developing a browser application
using our SDK. As such, we should provide some help in the form of "here's the basics of configuring
CORS support at the service level" in the README.

closes Azure#13149

Author: maorleger

sdk/template/template/README-TEMPLATE.md

@@ -97,6 +97,24 @@ const { DefaultAzureCredential } = require("@azure/identity");
 const client = new TextAnalyticsClient("<endpoint>", new DefaultAzureCredential());
 ```
 
+### JavaScript Bundle
+
+To use this client library in the browser, first you need to use a bundler. For details on how to do this, please refer to our [bundling documentation](https://aka.ms/AzureSDKBundling).
+
+### CORS
+
+> note to package authors: If the service supports CORS please use this section to describe how to enable CORS, otherwise delete this section. See an example below from Azure Storage:
+
+You need to set up [Cross-Origin Resource Sharing (CORS)](https://docs.microsoft.com/rest/api/storageservices/cross-origin-resource-sharing--cors--support-for-the-azure-storage-services) rules for your storage account if you need to develop for browsers. Go to Azure portal and Azure Storage Explorer, find your storage account, create new CORS rules for blob/queue/file/table service(s).
+
+For example, you can create the following CORS settings for local development. But please customize the settings carefully according to your requirements in a production environment.
+
+- Allowed origins: \*
+- Allowed verbs: DELETE,GET,HEAD,MERGE,POST,OPTIONS,PUT
+- Allowed headers: \*
+- Exposed headers: \*
+- Maximum age (seconds): 86400
+
 ## Key concepts
 
 ### TextAnalyticsClient