input: Write a python function to count the frequency of words in a list.
  assert word_frequency(['Good', 'Outlook', 'Good', 'Luck', 'Bad', 'Outlook', 'Good']) == {'Good': 3, 'Outlook': 2, 'Luck': 1, 'Bad': 1}
  assert word_frequency(['apple', 'banana', 'apple', 'orange', 'banana', 'apple']) == {'apple': 3, 'banana': 2, 'orange': 1}
  assert word_frequency(['one', 'two', 'three', 'two', 'three', 'three']) == {'one': 1, 'two': 2, 'three': 3}
output: def word_frequency(words):
      freq_dict = {}
      for word in words:
          if word in freq_dict:
              freq_dict[word] += 1
          else:
              freq_dict[word] = 1
      return freq_dict