docs: update for domain or email verification (#1145)

packages/mail/README.md

@@ -46,6 +46,10 @@ You may also use [yarn](https://yarnpkg.com/en/) to install.
 yarn add @sendgrid/mail
 ```
 
+## Verify identity
+Verify an email address or domain in the [Sender Authentication tab](https://app.sendgrid.com/settings/sender_auth/senders)
+Without this you will receive a 403 forbidden response when trying to send mail.
+
 <a name="quick-start"></a>
 # Quick Start, Hello Email
 
@@ -58,7 +62,7 @@ const sgMail = require('@sendgrid/mail');
 sgMail.setApiKey(process.env.SENDGRID_API_KEY);
 const msg = {
   to: 'test@example.com',
-  from: 'test@example.com',
+  from: 'test@example.com', // Use the email address or domain you verified above
   subject: 'Sending with Twilio SendGrid is Fun',
   text: 'and easy to do anywhere, even with Node.js',
   html: '<strong>and easy to do anywhere, even with Node.js</strong>',