fixup! remove coercing Weak<T> to Weak<U> for now, with TODO comm…

…ents

portable-atomic-util/src/lib.rs

@@ -48,7 +48,9 @@ Or set environment variable:
 RUSTFLAGS="--cfg portable_atomic_unstable_coerce_unsized" cargo ...
 ```
 
-- <a name="portable-atomic-unstable-coerce-unsized"></a>**`--cfg portable_atomic_unstable_coerce_unsized`**<br> support standard coercing of `Arc<T>` to `Arc<U>` and same for weak references
+- <a name="portable-atomic-unstable-coerce-unsized"></a>**`--cfg portable_atomic_unstable_coerce_unsized`**<br> support standard coercing of `Arc<T>` to `Arc<U>`
+
+<!-- TODO: add standard coercing of `Weak<T>` to `Weak<U>` as well, with testing & documentation updates -->
 
 This coercing requires Rust nightly to compile (with help from [unstable `CoerceUnsized` trait](https://doc.rust-lang.org/nightly/core/ops/trait.CoerceUnsized.html)).