docs: introduce gpustack and gguf-parser (#8873)

* readme: introduce gpustack

GPUStack is an open-source GPU cluster manager for running large
language models, which uses llama.cpp as the backend.

Signed-off-by: thxCode <thxcode0824@gmail.com>

* readme: introduce gguf-parser

GGUF Parser is a tool to review/check the GGUF file and estimate the
memory usage without downloading the whole model.

Signed-off-by: thxCode <thxcode0824@gmail.com>

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Signed-off-by: thxCode <thxcode0824@gmail.com>