[doc] Update x86 CPU-inference installation doc to reflect optionality of AVX512f

[sooraj-satheesh]

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
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Purpose

AVX512f is optional, see #5452 . updating the docs to reflect this. Solves #18660

Test Plan

Build the docker image with --build-arg VLLM_CPU_DISABLE_AVX512=true

Test Result

Container does not crash with Illegal Instruction on a cpu without avx512f.

(Optional) Documentation Update

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[gemini-code-assist]

Code Review

This pull request updates the x86 CPU inference installation documentation to reflect that the avx512f flag is now optional. The changes correctly mark the flag as optional and update the warning and build instructions. I've included a suggestion to improve the clarity and grammar of the updated warning message.

[gemini-code-assist]

There's an extra space before --build-arg which makes the indentation inconsistent with the other arguments. Please remove it for alignment.

Suggested change

	--build-arg VLLM_CPU_DISABLE_AVX512=false (default)|true \
	--build-arg VLLM_CPU_DISABLE_AVX512=true (default)|false \

[bigPYJ1151]

Hi @sooraj-satheesh In fact the AVX2 version is not recommend because it only has basic feature support. We recommend AVX512 version and only provides AVX512 pre-built image.

[sooraj-satheesh]

@bigPYJ1151 yes but the dockerfile supports building without it and it would reduce confusion to document this. The recommendation against it can also be added to the doc.