docs: Triton TRT-LLM user guide

[krishung5]

What does the PR do?

Enhance the TRT-LLM user experience by adding a comprehensive user guide to bridge the gap between Triton users and TRT-LLM functionalities.

Checklist

• PR title reflects the change and is of format <commit_type>: <Title>
• Changes are described in the pull request.
• Related issues are referenced.
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• Added test plan and verified test passes.
• Verified that the PR passes existing CI.
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• build
• ci
• docs
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• fix
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• refactor
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• test

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• closes GitHub issue: #xxx

[harryskim]

Looks great :)