add sleep for checking render success, add readme

cmd/cli/cli.go

@@ -14,6 +14,7 @@ import (
 	"os"
 	"path"
 	"strings"
+	"time"
 )
 
 func main() {
@@ -265,6 +266,7 @@ func job(id, outputLocation string) error {
 			fmt.Println("Video has completed rendering.")
 			break
 		}
+		time.Sleep(5 * time.Second)
 	}
 
 	// decode the video, it is in base64 and is expected to be a mp4