[issue41394] Document '_' in interpreter tutorial

[wyz23x2]

Change by wyz23x2 <wyz23x2 at 163.com>:


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pull_requests: +20792
pull_request: https://github.com/python/cpython/pull/21651

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41394>
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