readme: This model is converted from the original DKRR [repo](https://github.com/facebookresearch/FiD) and ported into Pyserini:
  
  ``` 
  @misc{izacard2020distilling,
        title={Distilling Knowledge from Reader to Retriever for Question Answering},
        author={Gautier Izacard and Edouard Grave},
        year={2020},
        eprint={2012.04584},
        archivePrefix={arXiv},
        primaryClass={cs.CL}
  }
  ```