Update based on rust-lang#116988 (the null address has the value 0)

Author: joshlf

library/core/src/ptr/mod.rs

@@ -66,10 +66,10 @@
 //! a separate allocated object), and `static` variables.
 //!
 //! It is guaranteed that an allocated object never spans more than `isize::MAX` bytes.
-//! An allocated object cannot contain [`null()`] and cannot contain the last (`usize::MAX`) byte
-//! of the address space. As a consequence, any address which is either in the allocated object or
-//! one byte past the last address in the allocated object can be computed without wrapping around
-//! the address space.
+//! An allocated object cannot contain [`null()`] (i.e., the address with the numerical value 0) and
+//! cannot contain the last (`usize::MAX`) byte of the address space. As a consequence, any address
+//! which is either in the allocated object or one byte past the last address in the allocated object
+//! can be computed without wrapping around the address space.
 //!
 //! [`null()`]: null
 //!