Describes an existing backup of a table.Show details from next link. https://docs.aws.amazon.com/ja_jp/cli/latest/reference/dynamodb/describe-backup.html
| aws dynamodb describe-backup \ |
| Restoring a DynamoDB Table from a Backup - Amazon DynamoDB : http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Backup.Tutorial.html |