Update changelog

Author: holly-hacker

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - impl embedded_hal_1::spi::SpiBus for SPI
 - impl embedded_hal_1::digital traits for Pins
 - Enable AF1 on GPIOE for pins [13, 14, 15] to support SPI communication
+- Allow creating open-drain output pins with pull-up or pull-down
 
 ### Fixed