input: Write a python function to search for a string in a list and return its index.
  assert search_string(['apple', 'banana', 'cherry'], 'banana') == 1
  assert search_string(['dog', 'cat', 'mouse'], 'elephant') == -1
  assert search_string(['red', 'blue', 'green'], 'green') == 2
output: def search_string(lst, target):
      try:
          return lst.index(target)
      except ValueError:
          return -1