Update Unreleased section of changelog

Author: tomhoule

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## Unreleased
 
+- [to be documnented] — A CLI and derive option to specify a module to import
+  custom scalar from. Thanks @miterst! ([PR](https://github.com/graphql-rust/graphql-client/pull/354))
+
 ## 0.9.0 - 2020-03-13
 
 ## Added