Add changelog for active-low pin change

Author: Morgan Roff

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+- Modified `OutputPin` behavior for active-low pins to match `InputPin` behavior.
 - Set default features to build both sysfs and cdev pin types.
 - Removed `Pin` export, use `CdevPin` or `SysfsPin`.
 - Increased the Minimum Supported Rust Version to `1.36.0` due to an update of `gpio_cdev`.