[docs] [issue33847] doc: Add '@' operator entry to index

[Andrés Delfino]

New submission from Andrés Delfino <adelfino at gmail.com>:

Currently, the index only refers to decorators for the @ symbol. PR adds entry for the matrix multiplication operator.

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assignee: docs at python
components: Documentation
messages: 319398
nosy: adelfino, docs at python
priority: normal
severity: normal
status: open
title: doc: Add '@' operator entry to index
type: enhancement
versions: Python 3.6, Python 3.7, Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue33847>
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