[docs] [issue21314] Document '/' in signatures

[Lysandros Nikolaou]

Change by Lysandros Nikolaou <lisandrosnik at gmail.com>:


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keywords: +patch, patch, patch
pull_requests: +9891, 9892, 9893
stage: needs patch -> patch review

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue21314>
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