add changelog for 254

Author: davidhewitt

CHANGELOG.md

@@ -11,6 +11,7 @@
 
 ### Changed
 - `Exec` binding `RustExtension` with `script=True` is deprecated in favor of `RustBin`. [#248](https://github.com/PyO3/setuptools-rust/pull/248)
+- Errors while calling `cargo metadata` are now reported back to the user [#254](https://github.com/PyO3/setuptools-rust/pull/254)
 - `quiet` option will now suppress output of `cargo metadata`. [#256](https://github.com/PyO3/setuptools-rust/pull/256)
 
 ### Fixed