title: how to add tokens in vocab.txt which decoded as [UNK] bert tokenizer
body: <p>i was decoding the tokenized tokens from <strong>bert tokenizer</strong> and it was giving <strong>[UNK]</strong> for € symbol. but i tried by add ##€ token in vocab.txt file. but it was not reflected in prediction result was same as previous it was giving [UNK] again. please let me know to solve this problem did i need to <strong>fine tune</strong> the model for again to reflect the changes in <strong>prediction</strong>. till now i was avoiding fine tuning again because it takes more than 10 hours.
  Thanks in advance</p>