Added SPI transactions to changelog

Author: ryankurte

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased]
 
 ### Added
+- `Transactional` SPI interface for executing groups of SPI transactions
 
 ### Changed
 
@@ -19,6 +20,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 - 10-bit addressing mode for I2C traits.
 - `try_set_state` method for `OutputPin` using an input `PinState` value.
+- `Transactional` interface for grouping SPI transactions
 
 ### Changed