input: Write a function to initialize a Chatbot class with greeting keywords and check for greetings in a user input sentence.
  assert Chatbot().check_for_greeting("Hello, how are you?") == True
  assert Chatbot().check_for_greeting("Goodbye!") == False
  assert Chatbot().check_for_greeting("Hey there!") == True
output: class Chatbot:
      def __init__(self):
          self.greetings = ["hello", "hi", "hey", "greetings", "salutations"]
  
      def check_for_greeting(self, sentence):
          sentence_words = sentence.lower().split()
          for word in sentence_words:
              if any(greet in word for greet in self.greetings):
                  return True
          return False