Added an example

example_test.go

@@ -0,0 +1,33 @@
+package gomail_test
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/go-gomail/gomail"
+)
+
+func ExampleSend() {
+	msg := gomail.NewMessage()
+	msg.SetHeader("From", "alex@example.com")
+	msg.SetHeader("To", "bob@example.com", "cora@example.com")
+	msg.SetAddressHeader("Cc", "dan@example.com", "Dan")
+	msg.SetHeader("Subject", "Hello!")
+	msg.SetBody("text/html", "Hello <b>Bob</b> and <i>Cora</i>!")
+
+	s := gomail.SendFunc(func(from string, to []string, msg io.WriterTo) error {
+		// Implements you email-sending function, for example by calling
+		// an API, or running postfix, etc.
+		fmt.Println("From:", from)
+		fmt.Println("To:", strings.Join(to, ", "))
+		return nil
+	})
+
+	if err := gomail.Send(s, msg); err != nil {
+		panic(err)
+	}
+	// Output:
+	// From: alex@example.com
+	// To: bob@example.com, cora@example.com, dan@example.com
+}