Multi-text files support for run_lm_finetuning
# 🚀 Feature request

Support multi-text files for run_lm_finetuning.

## Motivation

Currently, you support training from scratch but it only supports a single file. Usually, when we train from scratch we train a model using multi-text files, not a single text file.
It will be great to support multi-text file and maybe separate finetuning from training from scratch files.


This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
