optimizer hints: add notes for how to specify the table name in hints

[winoros]

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What is changed, added or deleted? (Required)

It's a little against intuition when we are specifying a table in the optimizer hints. So we add some notes to tell the user how to use it.

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[TomShawn]

what about English version?

I'll translate the approved Chinese version into English. First, let's have this PR approved.

[yiwen92]

Let's do a review and merge into branch, thx. @TomShawn

[TomShawn]

@winoros Please take a look at the comments above and address them. Thanks~

[qiancai]

Removed the needs-cherry-pick-release-6.3 label because the v6.3 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v6.3 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-6.4 label because the v6.4 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v6.4 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-6.6 label because the v6.6 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v6.6 and will no longer receive new updates.

[ti-chi-bot[bot]]

@winoros: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-verify	413f62cc88c90b39af88af7f04d83efc928c875a	link	true	/test pull-verify

Full PR test history. Your PR dashboard.

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