docs(CHANGES): Note strict mypy compliance

Author: tony

CHANGES

@@ -12,6 +12,14 @@ $ pip install --user --upgrade --pre libtmux
 
 - _Insert changes/features/fixes for next release here_
 
+## What's new
+
+- **Improved typings**
+
+  Now [`mypy --strict`] compliant ({issue}`383`)
+
+  [`mypy --strict`]: https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-strict
+
 ## Compatibility
 
 - Brought back python 3.7 and 3.8 support ({issue}`375`)