add pytest-dev#5250 changelog entry

EvanKepner · Sup3rGeo · commit 3a7c054627cf · 2019-05-30T19:22:08.000+02:00
diff --git a/changelog/5250.doc.rst b/changelog/5250.doc.rst
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+Expand docs on use of ``setenv`` and ``delenv`` with ``monkeypatch``.

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	`1`	+Expand docs on use of ``setenv`` and ``delenv`` with ``monkeypatch``.