input: Write a python function to count the frequency of each string in a list.
  assert count_strings(['a', 'b', 'c', 'a', 'b']) == {'a': 2, 'b': 2, 'c': 1}
  assert count_strings(['apple', 'banana', 'apple', 'orange', 'banana', 'apple']) == {'apple': 3, 'banana': 2, 'orange': 1}
  assert count_strings(['x', 'y', 'z', 'x', 'y', 'x']) == {'x': 3, 'y': 2, 'z': 1}
output: def count_strings(lst):
      freq_dict = {}
      for string in lst:
          if string in freq_dict:
              freq_dict[string] += 1
          else:
              freq_dict[string] = 1
      return freq_dict