input: Write a function to search a given string input from the user in a predefined list of strings. If a match is found, return "String matches", otherwise return "String doesn't match".
  assert search_string(["First", "Second", "Third"], "Sec") == "String matches"
  assert search_string(["First", "Second", "Third"], "Fourth") == "String doesn't match"
  assert search_string(["First", "Second", "Third"], "") == "String doesn't match"
output: def search_string(lst, user_input):
      for item in lst:
          if user_input in item:
              return "String matches"
      return "String doesn't match"