Adding NeMo Megatron Launcher integration inline in SteerLM documentation

[Zenodia]

What does this PR do ?

Adding NeMo Megatron Launcher integration inline in SteerLM documentation.
Add a one line overview of what this PR aims to accomplish.

Changelog

• Please update the CHANGELOG.md under next version with high level changes in this PR.
  @gshennvm please kindly advise if i should be updating changelog or if you would like to do this ?

Usage

• You can potentially add a usage example below for step 1 - converting hf llama2 ckpt (url :https://huggingface.co/meta-llama/Llama-2-70b-chat-hf/tree/main ) to .nemo format

# Add a code snippet demonstrating how to use this , example script running on oci 
python main.py launcher_scripts_path=<Path_to>/NeMo-Megatron-Launcher/launcher_scripts data_dir=<Path_to_the_folder_of_downloaded_HF_llama2_model_ckpts_and_files> base_results_dir=<Path_to_dir_of_job_logs> stages=[conversion_hf2nemo]

Before your PR is "Ready for review"

Pre checks:

• Make sure you read and followed Contributor guidelines
• Did you write any new necessary tests?
• Did you add or update any necessary documentation? Make sure to also update the NeMo Framework User Guide which contains the tutorials

Checklist when contributing a new algorithm

• Does the trainer resume and restore model state all states?
• Does the trainer support all parallelism techniques(PP, TP, DP)?
• Does the trainer support max_steps=-1 and validation?
• Does the trainer only call APIs defined in alignable_interface.py?
• Does the trainer have proper logging?

Additional Information

• Related to # (issue)

[gshennvm]

can you give a brief description of what nemo megatron launcher here?

[gshennvm]

mostly LGTM after resolving 1 more comment. Please make sure to also sign your commits before merge: https://github.com/NVIDIA/NeMo-Aligner/pull/84/checks?check_run_id=21083012106