docs: add deployment guidance for llm fine-tuning examples

[gmartini2000]

What does this PR do ?

Adds a README to the LLM fine-tuning examples directory that provides guidance on how to run recipes, clarifies the deprecation of finetune.py, and outlines next steps after training including basic deployment direction.

Changelog

• Added examples/llm_finetune/README.md
• Documented how to launch fine-tuning recipes using the automodel CLI
• Added note explaining that finetune.py is deprecated
• Added section describing how to use trained checkpoints after fine-tuning
• Added high-level deployment guidance and pointers to production workflows

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Additional Information

• Related to Path for deployment from customization examples #1216

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