the providers list is missing post_training. Add that column and `HuggingFace`, `TorchTune`, and `NVIDIA NEMO` as supported providers.
also point to these providers in docs/source/providers/index.md, and describe basic functionality
There are other missing provider types here as well, but starting with this
Signed-off-by: Charlie Doern <cdoern@redhat.com>
