input: Write a python function to scrape the first paragraph from a given URL and save it to a text file.
  assert scrape_and_save_paragraph('http://www.example.com') is None
  assert os.path.exists('content.txt')
output: import requests
  from bs4 import BeautifulSoup
  
  def scrape_and_save_paragraph(url):
      response = requests.get(url)
      soup = BeautifulSoup(response.content, 'html.parser')
      first_paragraph = soup.find('p').get_text()
      with open('content.txt', 'w') as file:
          file.write(first_paragraph)