Add lb change to changelog

Author: o-x-e-y

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ## Added
 
 - Derive `Default` for all measurement structs
+- make `lb` an option for mass in FromStr implementation (works the same as `lbs` does currently)
 
 ## [0.11.0]