Add suggestion from code review

Author: MorganR

CHANGELOG.md

@@ -8,7 +8,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased]
 
 ### Added
-- Added IoPin for swappable input/output pins.
+- Added `IoPin` trait for pins that can change between being inputs or outputs
+  dynamically.
 
 ### Changed
 - Swap PWM channel arguments to references