add description about proxy protocol (#13297)

[ti-chi-bot]

This is an automated cherry-pick of #13297

What is changed, added or deleted? (Required)

Refer to #13254. I was wrong about the behavior of proxy-protocol-networks. It actually accepts connections without Proxy Protocol for the addresses outside the list.

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• Delete files
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[ti-chi-bot]

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[Oreoxmt]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: e03c7a3