fix llama2_70b_lora broken link for Accelerate config file in the readme

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[ShriyaPalsamudram]

@hiwotadese can you also set gradient_clipping: 0.3 in the config? Details are in https://github.com/mlcommons/training/issues/765

[hiwotadese]

@ShriyaPalsamudram the config file here https://github.com/mlcommons/training/blob/master/llama2_70b_lora/configs/default_config.yaml already have the gradient_clipping: 0.3

[hiwotadese]

recheck