New folder structure (#1)

* Add new file org structure
* Add new notebooks to quickstart on Mac and via HF
* consolidate all images in a top-level folder
* Update main README
* Remove "news" section from main README
* rename HF Trainer finetuning notebook and add detail to README

Co-authored-by: Navyata Bawa <bnavyata@fb.com>
Co-authored-by: Hamid Shojanazeri <hamid.nazeri2010@gmail.com>