tikv-config: Fix wrong description

[TomShawn]

What is changed, added or deleted? (Required)

Fix wrong description in TiKV configuration file.

The description of compaction-readahead-size referred to https://docs.pingcap.com/zh/tidb/stable/tune-tikv-memory-performance#%E5%8F%82%E6%95%B0%E8%AF%B4%E6%98%8E.

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 (in Chinese).

• master (the latest development version)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)
• v4.0 (TiDB 4.0 versions)
• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

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

• This PR is translated from:
• Other reference link(s): 官方文档 TiKV 配置项 compaction-readahead-size 可能书写错误 #7038

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]

[REVIEW NOTIFICATION]

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• qiancai

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[Connor1996]

LGTM

[ti-chi-bot]

@Connor1996: Thanks for your review. The bot only counts approvals from reviewers and higher roles in list, but you're still welcome to leave your comments.

In response to this:

LGTM

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[TomShawn]

/remove-status LGT1
/status LGT2

[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: f97f58f

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #7054.