mail/smtprelay: Improve pkg-descr

mail/smtprelay/pkg-descr

@@ -1,4 +1,6 @@
-Simple Golang SMTP relay/proxy server that accepts mail via
-SMTP and forwards it directly to another SMTP server.
+Simple Golang SMTP relay/proxy server that accepts mail via SMTP
+and forwards it directly to another SMTP server. It supports TLS,
+STARTTLS, plain SMTP, can do authentication and various sender
+and receiver checks.
 
 WWW: https://code.bluelife.at/decke/smtprelay