Add hardware plugins to installation doc

[mgoin]

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

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Test Plan

Test Result

(Optional) Documentation Update

[github-actions]

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[gemini-code-assist]

Code Review

This pull request adds documentation for hardware plugins, which is a valuable addition. However, the new documentation for Intel Gaudi creates a potential point of confusion for users, as there is now information for both in-tree and plugin-based support without any clarification on which to use. I have added a review comment with a suggestion to resolve this ambiguity.

[youkaichao]

thanks for adding them!