input: Write a python function to search for documents containing a specific keyword.
  assert search(["hello world", "python programming", "world of code"], "world") == ["hello world", "world of code"]
  assert search(["apple pie", "banana split", "cherry tart"], "banana") == ["banana split"]
  assert search(["open source", "source code", "closed source"], "source") == ["open source", "source code", "closed source"]
output: def search(documents, keyword):
      return [doc for doc in documents if keyword in doc]