Add to ONNX docs (#13048)
Add to ONNX docs (#13048)

* Add to ONNX docs

* Add MBART example

* Update docs/source/serialization.rst

Co-authored-by: Sylvain Gugger <222c4d44cc8ec39802c192ed0aa3f97cdb77ff4e@users.noreply.github.com>

Co-authored-by: Sylvain Gugger <222c4d44cc8ec39802c192ed0aa3f97cdb77ff4e@users.noreply.github.com>
huggingface/transformers,huggingface/transformers,huggingface/transformers,huggingface/transformers