dumpling: clarify description about --csv-separator

[pepezzzz]

--csv-separator $(echo -e "\x01")

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add --csv-separator $(echo -e "\x01") commets

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[lance6716]

感觉这个描述要结合更详细的用法，能让人看懂

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-11-26 10:30:41.357188742 +0000 UTC m=+698805.006383199: ☑️ agreed by lance6716.

[hfxsd]

/approve

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #21128.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #21129.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.4: #21130.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #21131.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #21132.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #21133.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #21134.
But this PR has conflicts, please resolve them!