Add link to rust-lang/rust PR for v0.57.0 changelog

Author: aDotInTheVoid

CHANGELOG.md

@@ -2,7 +2,8 @@
 # [v0.57.0](https://github.com/rust-lang/rustdoc-types/releases/tag/v0.57.0) - 2025-11-22
 
 **Breaking Change**: Add `ExternalCrate::path` field.
-This can be used to enable robust resolution of external crates.
+This can be used to enable robust resolution of external crates
+([rust#149043](https://github.com/rust-lang/rust/pull/149043)).
 
 - Format Version: 57
 - Upstream Commit: [`361af821ab169a98e9fc1db5d3a57978504ed379`](https://github.com/rust-lang/rust/commit/361af821ab169a98e9fc1db5d3a57978504ed379)