input: Write a function to crawl a website for phone numbers and return a list of found phone numbers in the format of "XXX-XXX-XXXX". If the website is "www.example.com", the function should send a GET request to the website, extract all phone numbers using a regular expression, and return them as a list. If no phone numbers are found, the function should return an empty list.
  
  assert crawl_website_for_phone_numbers('www.example.com')==['123-456-7890', '987-654-3210']
output: import requests
  import re
  
  def crawl_website_for_phone_numbers(url):
      response = requests.get(f"http://{url}")
      phone_numbers = re.findall(r'\b\d{3}-\d{3}-\d{4}\b', response.text)
      return phone_numbers