add changelog entry

Author: Emilgardis

CHANGELOG.md

@@ -5,6 +5,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+- #684 - Enable cargo workspaces to work from any path in the workspace, and make path dependencies mount seamlessly.
 - #494 - Parse Cargo's --manifest-path option to determine mounted docker root
 - #709 - Update Emscripten targets to `emcc` version 3.1.10
 - #707, #708 - Set `BINDGEN_EXTRA_CLANG_ARGS` environment variable to pass sysroot to `rust-bindgen`