docs: def check_requirements_file(req_file, skip_packages):
      """Return list of outdated requirements.
  
      Args:
          req_file (str): Filename of requirements file
          skip_packages (list): List of package names to ignore.
      """
      reqs = read_requirements(req_file)
      if skip_packages is not None:
          reqs = [req for req in reqs if req.name not in skip_packages]
      outdated_reqs = filter(None, [check_req(req) for req in reqs])
      return outdated_reqs