input: Write a python function to join a list of words into a single string separated by spaces.
  assert join_words(["Hello", "World", "!"]) == "Hello World !"
  assert join_words(["Python", "is", "awesome"]) == "Python is awesome"
  assert join_words(["Join", "these", "words"]) == "Join these words"
output: def join_words(words):
      return " ".join(words)