Modify parallel hashagg spill doc

[xzhangxian1008]

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[xzhangxian1008]

/cc @Oreoxmt

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[LGTM Timeline notifier]

Timeline:

• 2024-06-17 08:24:35.476024092 +0000 UTC m=+16801.961512923: ☑️ agreed by Oreoxmt.
• 2024-06-21 07:25:21.908869861 +0000 UTC m=+358848.394358691: ☑️ agreed by qiancai.

[Oreoxmt]

/unhold
/approve

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