ctl: add a note for all ctl docs (#6096)

[ti-srebot]

cherry-pick #6096 to release-3.0
You can switch your code base to this Pull Request by using git-extras:

# In docs-cn repo:
git pr https://github.com/pingcap/docs-cn/pull/6098

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/docs-cn.git pr/6098:release-3.0-ab487f7ac001

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[ti-srebot]

@yikeke you're already a collaborator in bot's repo.

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• yikeke

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[yikeke]

/merge

[ti-chi-bot]

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

Commit hash: 5ec282c

[yikeke]

/merge

[ti-chi-bot]

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

Commit hash: 165c394