def chain_add(word, next_word)
    markov_chains[word] ||= Hash.new(0)
    markov_chains[word][next_word] += 1
  end
def chain_add(word, next_word)
    markov_chains[word] ||= Hash.new(0)
    markov_chains[word][next_word] += 1
  end
add a word/next_word pair to @markov_chains