Remove outdated command directions and use in tests

[muellerzr]

Since torch.distributed.launch is deprecated, finds all cases of launch and replaces with run/torchrun

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Thanks! In the examples we should mention that for older PyTorch versions, user should use torch.distributed.launch no?

[muellerzr]

@sgugger changed it to be:

    * With PyTorch launcher only (`torch.distributed.launch` can be used in older versions of PyTorch)
        ```bash
        python -m torchrun --nproc_per_node 2 \
            --use_env \
            --node_rank 0 \
            --master_addr master_node_ip_address \
            ./nlp_example.py  # On the first server
       ```

in the respective areas in the README.md