[docs] [issue27825] Make the documentation for statistics' data argument clearer.

[Steven D'Aprano]

Changes by Steven D'Aprano <steve+python at pearwood.info>:


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assignee: docs at python -> steven.daprano
nosy: +steven.daprano

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue27825>
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