Update information on using Gmail when 2FA is in use [ci skip]

guides/source/action_mailer_basics.md

@@ -781,7 +781,8 @@ config.action_mailer.smtp_settings = {
   enable_starttls_auto: true  }
 ```
 Note: As of July 15, 2014, Google increased [its security measures](https://support.google.com/accounts/answer/6010255) and now blocks attempts from apps it deems less secure.
-You can change your gmail settings [here](https://www.google.com/settings/security/lesssecureapps) to allow the attempts or
+You can change your gmail settings [here](https://www.google.com/settings/security/lesssecureapps) to allow the attempts. If your Gmail account has 2-factor authentication enabled,
+then you will need to set an [app password](https://myaccount.google.com/apppasswords) and use that instead of your regular password. Alternatively, you can
 use another ESP to send email by replacing 'smtp.gmail.com' above with the address of your provider.
 
 Mailer Testing