[issue41411] Improve and consolidate f-strings docs

[Ama Aje My Fren]

Change by Ama Aje My Fren <amaajemyfren at gmail.com>:


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pull_requests: +20825
pull_request: https://github.com/python/cpython/pull/21681

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41411>
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