Add ability to pull information from Transformers docs

[NielsRogge]

Hi,

This library looks great already. It would be awesome if we can leverage it when adding new models to the Transformers library. For now, model cards are created manually (after pushing the checkpoints to the hub).

We typically duplicate things from the documentation into the model card (like the abstract of the paper, a code snippet showcasing basic usage, the URL of the paper, short description of the model, etc.).

For instance, check the ViT docs, which is then used in the model card of a ViT checkpoint.

So ideally, we could use this library in the conversion scripts, where we also add the model card when pushing to the model.