instruction: Write Go code to go by example: waitgroups
output: ```dockerfile
  $ go run waitgroups.go
  Worker 5 starting
  Worker 3 starting
  Worker 4 starting
  Worker 1 starting
  Worker 2 starting
  Worker 4 done
  Worker 1 done
  Worker 2 done
  Worker 5 done
  Worker 3 done
  ```