[Usability] Break README.md into sections and remove GETTING-STARTED.md

[orionr]

Did some significant reordering and revamp on README.md and removed GETTING-STARTED.md. We still need to support flags like --help, but this gets us much closer to install expectations and also matches a bit more to best practices as you'll see in torchtune at https://github.com/pytorch/torchtune/blob/main/README.md

[mikekgfb]

LGTM.

Let's make sure we don't lose content.

Please also pull in content from https://github.com/pytorch/torchat/pull/170/commits which has updated for GGUF file loading and status that was not yet landed in the README.md

[orionr]

Yup - didn't remove any content for now, although I think we'll ned to trim it down later. Are the test failures any concern @mikekgfb ? Looks unrelated.

[mikekgfb]

Test failures are always a concern! The biggest issue right now is the segmentation fault that happens reproducibly.

Possibly the dso we build is broken because the rest is Python which should not have unsafe references. Will need help from compiler team as discussed (the incorrect results from AOTI are another item)