Add local agent (`Pi` + `llama.cpp`) guide (#2248)
* add Pi + llama.cpp guide
* improve wording
* nit
* Apply suggestions from code review
Co-authored-by: Julien Chaumond <julien@huggingface.co>
Co-authored-by: Pedro Cuenca <pedro@huggingface.co>
* add a small section for llama-agent
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Co-authored-by: Julien Chaumond <julien@huggingface.co>
Co-authored-by: Pedro Cuenca <pedro@huggingface.co>
