docs: def write_requirements(reqs_linenum, req_file):
      """Writes a list of req objects out to a given file."""
      with open(req_file, 'r') as input:
          lines = input.readlines()
  
      for req in reqs_linenum:
          line_num = int(req[1])
  
          if hasattr(req[0], 'link'):
              lines[line_num - 1] = '{}\n'.format(req[0].link)
          else:
              lines[line_num - 1] = '{}\n'.format(req[0])
  
      with open(req_file, 'w') as output:
          output.writelines(lines)