Update README.md

Merge pull request #39 from MihaelIsaev/master

Fix `IncomingMessage` model and update to Vapor4 RC with Swift 5.2

Merge pull request #37 from MihaelIsaev/master

Upgrade to Vapor4

Merge pull request #35 from saicu/master

Multiple Domain Configuration

Merge pull request #34 from saicu/master

fix for sending without template data

Merge pull request #32 from saicu/master

Mailgun templates

Merge pull request #31 from madsodgaard/feature/eu-support

Add support for region selection

Merge pull request #29 from AAAstorga/master

Add inline support

Merge pull request #20 from rafiki270/master

readme update for the new code

Merge pull request #17 from MihaelIsaev/patch-1

Implement replyTo