Add an example for sessions + securecookie. Relative: http://support.iris-go.com/d/29-mark-cookie-for-session-as-secure

Former-commit-id: 10c30aabdf6b8fa59457ed8296b3e87108d3861c

_examples/examples/sessions/main.go

@@ -42,7 +42,8 @@ func logout(ctx *iris.Context) {
 func main() {
 	app := iris.New()
 	app.Adapt(httprouter.New())
-
+	// Look https://github.com/kataras/iris/tree/v6/adaptors/sessions/_examples for more features,
+	// i.e encode/decode and lifetime.
 	sess := sessions.New(sessions.Config{Cookie: key})
 	app.Adapt(sess)