input: Write a python function to count the number of words and calculate the average word length in a sentence.
  assert count_words("Hello world") == (2, 5.0)
  assert count_words("The quick brown fox jumps over the lazy dog") == (9, 3.888888888888889)
  assert count_words("Python is awesome") == (3, 5.333333333333333)
output: def count_words(sentence):
      words = sentence.split()
      num_words = len(words)
      avg_length = sum(len(word) for word in words) / num_words
      return num_words, avg_length