pointer to transformer (big) model
# 🌟 New model addition

## Model description

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Hi, needed a pointer on how to instantiate a Transformer-big from the original Vaswani et. al. paper (Attention Is All You Need). I could only find versions of Transformer-like architectures, so would be useful if this could also be added.

## Open source status

* [x] the model implementation is available: (give details): https://research.google/pubs/pub46201/
* [ ] the model weights are available: (give details)
* [ ] who are the authors: (mention them, if possible by @gh-username)

@anirudt  Can I work on this issue?<|||||>Any leads on this?
