Adding link to existing Fine-tuning example in Notebooks

[jimburtoft]

Phil had a notebook on fine tuning in here that wasn't listed in the Readme.

Before submitting

• [x ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

[JingyaHuang]

Oh, I see that is not listed in the doc neither:https://huggingface.co/docs/optimum-neuron/en/tutorials/notebooks.
Nor in the doc overview: https://huggingface.co/docs/optimum-neuron/en/tutorials/fine_tune_llama_7b @philschmid .

Would you mind adding it to:

• https://github.com/huggingface/optimum-neuron/blob/main/docs/source/tutorials/overview.mdx#overview
  and
• https://github.com/huggingface/optimum-neuron/blob/main/docs/source/tutorials/notebooks.mdx
  as well? Thank you so much!

[jimburtoft]

@JingyaHuang I can look into that later this week. Should all three have all the links on them? I should be adding more examples, so just let me know where they need to be updated.

[JingyaHuang]

LGTM, no prob, I can doc a quick PR to update the doc. Thanks @jimburtoft !