Model ladder has no documentation

[IanMagnusson]

📚 The doc issue

It would be great if there was some kind of a readme for the model ladder (#649). As far as I know there is currently no documentation for this.

I believe this is the entry point? https://github.com/allenai/OLMo/blob/main/scripts/ladder.py

@taidnguyen, @dwadden, and I will likely want to run data mix experiments in the future that make use of the model ladder for standardization and having some basic documentation would avoid having each of us have to come bug people for 1:1 explanations.

Suggest a potential alternative/fix

No response

[IanMagnusson]

Intending to address this with #708