Add CHANGELOG entry

Author: mediremi

CHANGELOG.md

@@ -32,6 +32,7 @@
 - AST: use `Typ.arrows` for creation, after the refactoring of arrow types. https://github.com/rescript-lang/rescript/pull/7662
 - Don't skip Stdlib docstring tests. https://github.com/rescript-lang/rescript/pull/7694
 - Remove all leftovers of pinned-dependencies handling. https://github.com/rescript-lang/rescript/pull/7686
+- Add `rust-version` field to Rewatch's `Cargo.toml`. https://github.com/rescript-lang/rescript/pull/7701
 
 #### :bug: Bug fix