fix docs; add numina tasks (#79)

- Fixes some broken links after #77 . `skythought_evals` has been renamed to `evals` and the package name is `skythought`.
- Added separate yamls for Numina for a better quickstart experience. Ideally, we shouldn't have to keep adding yamls for all the training datasets in the evaluation library, and should instead provide APIs for standalone scripts. For now we do this to support reproduction of Sky-T1 models.

Signed-off-by: SumanthRH <sumanthrh@anyscale.com>