Add example in the project. #13

import (
	"fmt"
	"log"
	"os"

	"github.com/phoops/ngsiv2/client"
)

func main() {
	url := os.Getenv("ORION_BROKER")
	cli, err := client.NewNgsiV2Client(client.SetUrl(url))
	if err != nil {
		log.Fatalln(err)
	}

	e, err := cli.RetrieveEntity("urn:ngsi-ld:Product:001", client.RetrieveEntitySetType("Product"))
	if err != nil {
		log.Fatalln(err)
	}
	
	b, _ := e.MarshalJSON()
	fmt.Println(string(b))
}