Update QuickStart to Something Usable

[StellaAthena]

It was raised in https://github.com/EleutherAI/gpt-neox/issues/482?notification_referrer_id=NT_kwDOAPKasLMyODMxNjY1ODU3OjE1ODk5MzEy#issuecomment-996767144 that the QuickStart default settings aren’t actually intended to be used to train a model to completion, and that this is confusing to new users. We should create a better QuickStart demo, perhaps with a dedicated config file.