message: README: add another bug Miri found
diff: @@ -245,6 +245,7 @@ Violations of [Stacked Borrows] found that are likely bugs (but Stacked Borrows
  * [`BTreeMap` creating mutable references that overlap with shared references](https://github.com/rust-lang/rust/pull/58431)
  * [`LinkedList` creating overlapping mutable references](https://github.com/rust-lang/rust/pull/60072)
  * [`Vec::push` invalidating existing references into the vector](https://github.com/rust-lang/rust/issues/60847)
  +* [`align_to_mut` violating uniqueness of mutable references](https://github.com/rust-lang/rust/issues/68549)
  ## License
  