remark that the rules are unfinished

Author: RalfJung

src/libcore/mem.rs

@@ -1230,6 +1230,8 @@ impl<T> MaybeUninit<T> {
     /// let x_vec = unsafe { &*x.as_ptr() };
     /// // We have created a reference to an uninitialized vector! This is undefined behavior.
     /// ```
+    /// (Notice that the rules around referenced to uninitialized data are not finalized yet, but
+    /// until they are, it is advisable to avoid them.)
     #[unstable(feature = "maybe_uninit", issue = "53491")]
     #[inline(always)]
     pub fn as_ptr(&self) -> *const T {
@@ -1266,6 +1268,8 @@ impl<T> MaybeUninit<T> {
     /// let x_vec = unsafe { &mut *x.as_mut_ptr() };
     /// // We have created a reference to an uninitialized vector! This is undefined behavior.
     /// ```
+    /// (Notice that the rules around referenced to uninitialized data are not finalized yet, but
+    /// until they are, it is advisable to avoid them.)
     #[unstable(feature = "maybe_uninit", issue = "53491")]
     #[inline(always)]
     pub fn as_mut_ptr(&mut self) -> *mut T {