tiup: Update THP docs

[dveeden]

What is changed, added or deleted? (Required)

• The current advise doesn't always make a reboot-safe change (it only changes the running configuration).

See also:

• https://access.redhat.com/solutions/46111
• https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/8/html/managing_monitoring_and_updating_the_kernel/assembly_making-persistent-changes-to-the-grub-boot-loader_managing-monitoring-and-updating-the-kernel#proc_adding-and-removing-arguments-from-a-grub-2-menu-entry_assembly_making-persistent-changes-to-the-grub-boot-loader

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• master (the latest development version)
• v9.0 (TiDB 9.0 versions)
• v8.5 (TiDB 8.5 versions)
• v8.4 (TiDB 8.4 versions)
• v8.3 (TiDB 8.3 versions)
• v8.1 (TiDB 8.1 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)

What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s):

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-23 02:05:21.394699773 +0000 UTC m=+319248.725619177: ☑️ agreed by hfxsd.
• 2025-01-23 06:31:00.575455616 +0000 UTC m=+335187.906375019: ☑️ agreed by breezewish.

[hfxsd]

/approve

[ti-chi-bot]

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #20139.