Tutorial for running a training on AirGapped cluster with singularity

**Is your feature request related to a problem? Please describe.**
Many national clusters are based on slurm and do not support docker containers, but only singularity. This makes more challenging preparing the environment and then running the experiments (need to download the models and data in advance).

**Describe the solution you'd like**
I am attaching a guide I prepared to support a reasearch group working with Megatron-LM.

**Additional context**
I am an SA at NVIDIA supporting HER so this is a very common problem among people I work with.

[mt-slm-to-publish.md](https://github.com/user-attachments/files/22795262/mt-slm-to-publish.md)