[Docs] Add Liger-Kernel usage to SFTTrainer page

[ryankert01]

What does this PR do?

Document a famous package Liger-Kernel usage in SFT trainer page that can can effectively increase multi-GPU training throughput by 20% and reduces memory usage by 60%.

Reference: Liger-Kernel

followup of: huggingface/transformers#32860

fixed #184

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[lewtun]

Thanks a lot for the docs - they look great!

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.