Update readme

README.md

@@ -1,3 +1,10 @@
 # smtp-proxy
 
-Simple Go SMTP relay/proxy server
+Simple Go SMTP relay/proxy server that accepts mails via SMTP
+and forwards directly to another SMTP server.
+
+## Main features
+
+* STARTTLS/TLS support
+* IPv6 support
+* Forward to GMail, MailGun or any other SMTP server