hcl: Fix the simple example in the README

Author: Mark Foster

README.md

@@ -33,11 +33,25 @@ package main
 
 import (
 	"log"
+
 	"github.com/hashicorp/hcl/v2/hclsimple"
 )
 
 type Config struct {
-	LogLevel string `hcl:"log_level"`
+	IOMode  string        `hcl:"io_mode"`
+	Service ServiceConfig `hcl:"service,block"`
+}
+
+type ServiceConfig struct {
+	Protocol   string          `hcl:"protocol,label"`
+	Type       string          `hcl:"type,label"`
+	ListenAddr string          `hcl:"listen_addr"`
+	Processes  []ProcessConfig `hcl:"process,block"`
+}
+
+type ProcessConfig struct {
+	Type    string   `hcl:"type,label"`
+	Command []string `hcl:"command"`
 }
 
 func main() {