Add StableLM as an example to the README

[StellaAthena]

https://github.com/Stability-AI/StableLM

[snirbenyosef]

Waiting for it :)
hope to see some example on how to fine-tune the model using gpt-neox

[Quentin-Anthony]

Bumping this up in priority due to the 3B release: https://github.com/Stability-AI/StableLM#stablelm-3b-4e1t

[Quentin-Anthony]

• Add configs for StableLM models
• Add README section describing how to use the StableLM models in gpt-neox for finetuning/inference/pre-training