docs: Update README.md to explicitly state that 'send()' returns a pr…

…omise (#989)

packages/mail/README.md

@@ -63,7 +63,9 @@ const msg = {
   text: 'and easy to do anywhere, even with Node.js',
   html: '<strong>and easy to do anywhere, even with Node.js</strong>',
 };
-sgMail.send(msg);
+sgMail.send(msg)
+.then((res) => //resolved )
+.catch((error) => //rejected )
 ```
 
 After executing the above code, you should have an email in the inbox of the recipient. You can check the status of your email [in the UI](https://app.sendgrid.com/email_activity?). Alternatively, we can post events to a URL of your choice using our [Event Webhook](https://sendgrid.com/docs/API_Reference/Webhooks/event.html). This gives you data about the events that occur as Twilio SendGrid processes your email.
@@ -104,4 +106,4 @@ Please see our [troubleshooting guide](https://github.com/sendgrid/sendgrid-node
 
 @sendgrid/mail is maintained and funded by Twilio SendGrid, Inc. The names and logos for @sendgrid/mail are trademarks of Twilio SendGrid, Inc.
 
-![Twilio SendGrid Logo](https://github.com/sendgrid/sendgrid-python/raw/master/twilio_sendgrid_logo.png)
+![Twilio SendGrid Logo](https://github.com/sendgrid/sendgrid-python/raw/master/twilio_sendgrid_logo.png)