[issue37779] configparser: add documentation about several read() behaviour

[SilentGhost]

Change by SilentGhost <ghost.adh at runbox.com>:


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components: +Cross-Build -Library (Lib)
nosy: +Alex.Willmer
stage:  -> needs patch
type: enhancement -> behavior
versions: +Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37779>
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