docs(changelog): document async-std-rt deprecation as breaking change and reqwless blocker

Author: e-desouza

CHANGELOG.md

@@ -12,6 +12,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [[Unreleased]]
 
+### Breaking Changes
+
+- **`async-std-rt` feature deprecated**: The `async-std` crate has been officially discontinued (RUSTSEC-2025-0052). The `async-std-rt` feature now emits a `compile_error!` directing users to migrate to `smol-rt` as a drop-in replacement. Code using `async-std-rt` will no longer compile until the feature is updated.
+
+### Known Blockers
+
+- **`atomic-polyfill` advisory (RUSTSEC-2023-0089)**: Cannot be resolved yet. `reqwless` 0.13.0 pins `embedded-tls` 0.17.0 which transitively depends on `atomic-polyfill`. This is blocked upstream and will be resolved when `reqwless` upgrades its `embedded-tls` dependency.
+
 ## [[v1.0.0]]
 
 - Initial production release