fixed prepare_dataset path in 0_to_litgpt.md

[EswarDivi]

No description provided.

[rasbt]

Thanks, much appreciated @EswarDivi !

[Andrei-Aksionov]

Hey @rasbt
VSCode has built-in link validator which is disabled by default. It wouldn't help in this case, but it found another issue:

 
**More information and additional resources**

- [tutorials/convert_lit_models](tutorials/convert_lit_models.md): Tutorial on converting LitGPT weights

Since tutorials are in the same folder, the path should be ./convert_lit_models.md. (Or just convert_lit_models.md also works).

But it checks only local link, for the external link you need some another extension.

[Andrei-Aksionov]

I decided to create a PR with fixes: #1219