NEWS bullet about altrep.hpp

Author: DavisVaughan

NEWS.md

@@ -1,5 +1,8 @@
 # cpp11 (development version)
 
+* Because cpp11 now requires R >=4.0.0 and ALTREP is always available, the
+  `cpp11/altrep.hpp` file is no longer useful. Please avoid using `#include "cpp11/altrep.hpp"` as we'd like to remove this file in the future (#411).
+
 * cpp11 now requires R >=4.0.0, in line with the
   [tidyverse version policy](https://www.tidyverse.org/blog/2019/04/r-version-support/) (#411).