docs(Changelog): Adapt changelog fragment

I noticed that the number didn't correspond to the PR #, so I renamed
the file. Also modified the content to properly reflect the changes.

Author: iron3oxide

changelog.d/950.change.rst

@@ -0,0 +1,4 @@
+validators._in() now includes the default argument
+"verbose_value_error=False". If set to True, the
+ValueError raised in _InValidator includes the attribute,
+options and value in addition to the error message.