read: fix doc comment

Author: RalfJung

src/libstd/io/mod.rs

@@ -511,8 +511,8 @@ pub trait Read {
     ///
     /// Correspondingly, however, *callers* of this method may not assume any guarantees
     /// about how the implementation uses `buf`. The trait is safe to implement,
-    //  so it is possible that the code that's supposed to write to the buffer might also read
-    //  from it. It is your responsibility to make sure that `buf` is initialized
+    /// so it is possible that the code that's supposed to write to the buffer might also read
+    /// from it. It is your responsibility to make sure that `buf` is initialized
     /// before calling `read`. Calling `read` with an uninitialized `buf` (of the kind one
     /// obtains via [`MaybeUninit<T>`]) is not safe, and can lead to undefined behavior.
     ///