Merge pull request rust-lang#4250 from asomers/patch-1

Add another Miri-detected bug to README.md

Author: RalfJung

src/tools/miri/README.md

@@ -565,6 +565,7 @@ Definite bugs found:
 * [Occasional memory leak in `std::mpsc` channels](https://github.com/rust-lang/rust/issues/121582) (original code in [crossbeam](https://github.com/crossbeam-rs/crossbeam/pull/1084))
 * [Weak-memory-induced memory leak in Windows thread-local storage](https://github.com/rust-lang/rust/pull/124281)
 * [A bug in the new `RwLock::downgrade` implementation](https://rust-lang.zulipchat.com/#narrow/channel/269128-miri/topic/Miri.20error.20library.20test) (caught by Miri before it landed in the Rust repo)
+* [Mockall reading unintialized memory when mocking `std::io::Read::read`, even if all expectations are satisfied](https://github.com/asomers/mockall/issues/647) (caught by Miri running Tokio's test suite)
 
 Violations of [Stacked Borrows] found that are likely bugs (but Stacked Borrows is currently just an experiment):