Enhance the doc

Author: vstinner

Doc/c-api/hash.rst

@@ -53,7 +53,8 @@ See also the :c:member:`PyTypeObject.tp_hash` member.
 
 .. c:function:: Py_hash_t Py_HashPointer(const void *ptr)
 
-   Hash a pointer.
+   Hash a pointer value: process the pointer value as an integer (cast it to
+   ``uintptr_t`` internally). The pointer is not dereferenced.
 
    The function cannot fail: it cannot return ``-1``.