Grammar change

src/doc/book/unsized-types.md

@@ -55,6 +55,7 @@ struct Foo<T: ?Sized> {
 }
 ```
 
-This `?Sized`, read as “T may or may not be `Sized`”, allowing us to match both
-constant size and unsized types. All generic type parameters implicitly have
-the `Sized` bound, so `?Sized` can be used to opt-out of the implicit bound.
+This `?Sized`, read as “T may or may not be `Sized`”, which allows us to match
+both constant size and unsized types. All generic type parameters implicitly
+have the `Sized` bound, so `?Sized` can be used to opt-out of the implicit
+bound.