Improve wording on layout.pointer.unsized

Changing this sentence to use "are", as this PR does, is correct.  But
it's clear too why the original had said "is", as with the change
it reads a bit awkwardly.  Adding the work "each" corrects this,
so let's do that.

Author: traviscross

src/type-layout.md

@@ -58,7 +58,7 @@ r[layout.pointer.thin]
 Pointers to sized types have the same size and alignment as `usize`.
 
 r[layout.pointer.unsized]
-Pointers to unsized types are sized. The size and alignment of a pointer to an unsized type are guaranteed to be greater than or equal to the size and alignment of a pointer to a sized type.
+Pointers to unsized types are sized. The size and alignment of a pointer to an unsized type are each guaranteed to be greater than or equal to those of a pointer to a sized type.
 
 > [!NOTE]
 > Though you should not rely on this, all pointers to <abbr title="Dynamically Sized Types">DSTs</abbr> are currently twice the size of the size of `usize` and have the same alignment.