Update changelog with unreleased 8.1.1 changes
Changelog
---------
+8.1.1 (Unreleased)
+******************
+
+Changes:
+
+* Set ``python_requires>=3.7.2`` in package metadata (:pr:`692`).
+ Thanks :user:`kasium` for the PR.
+
8.1.0 (2022-01-12)
******************
