update readme

README.md

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 The **email plugin** for [Grav](http://github.com/getgrav/grav) adds the ability to send email utilizing the `symfony/mailer` package. This is particularly useful for the **admin** and **login** plugins.
 
+> Version 4.0 replaced the old deprecated `SwiftMailer` library with `Symfony/Mailer` package.  This is a modern and well supported library that also has the capability to support 3rd party libraries such as  `SendGrid`, `MailJet`, `MailGun`, `MailChimp`, etc.
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 # Installation
 
 The email plugin is easy to install with GPM.
@@ -40,12 +42,6 @@ The first setting you'd likely change is your `Email from` / `Email to` names an
 
 Also, you'd likely want to setup a SMTP server instead of using PHP Mail, as the latter is not 100% reliable and you might experience problems with emails.
 
-Valid values for `auth_mode` include `plain`, `login`, `cram-md5`, or `null`.
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-> NOTE: `engine: mail` has been deprecated from the SwiftMail library that this plugin uses as it does not function at all.  Please use `smtp` if at all possible, and `sendmail` if SMTP is not an option.
-> 
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 ## 3rd Party Plugin Support
 
 Along with the **Email** `v4.0` release, there has also been several custom provider plugins released to provide support for `SMTP`, `API`, and sometimes even `HTTPS` support for 3rd party providers such as **Sendgrid**, **MailJet**, **MailGun**, **Amazon SES**, **Mailchimp/Mandrill**, and others!  `API` or `HTTPS` will provide a faster email sending experience compared to `SMTP` which is an older protocol and requires more back-and-forth negotiation and communication compared to the single-request of `API` or `HTTPS` solutions.