Rollup merge of #61273 - RalfJung:maybe-uninit, r=Centril

mention that MaybeUninit is a bit like Option

Author: Centril

src/libcore/mem.rs

@@ -966,6 +966,9 @@ impl<T: ?Sized> DerefMut for ManuallyDrop<T> {
 ///
 /// The compiler then knows to not make any incorrect assumptions or optimizations on this code.
 ///
+/// You can think of `MaybeUninit<T>` as being a bit like `Option<T>` but without
+/// any of the run-time tracking and without any of the safety checks.
+///
 /// ## out-pointers
 ///
 /// You can use `MaybeUninit<T>` to implement "out-pointers": instead of returning data