Update lib.rs

Author: Qelxiros

library/core/src/lib.rs

@@ -323,6 +323,7 @@ pub mod cmp;
 pub mod convert;
 pub mod default;
 pub mod error;
+#[unstable(feature = "sliceindex_wrappers", issue = "146179")]
 pub mod index;
 pub mod marker;
 pub mod ops;