Ability to add a comment in the twilio response

### Issue Summary
I would like the ability to add a comment within the xml twiml response,  as in 
```
<Response>

</Response>
```

### Steps to Reproduce
1. n/a

### Code Snippet
proposed syntax would be something like
```php
$response->comment("this is a comment");
```

### Technical details:
* twilio-php version: 
* php version: 8.2