Add example in method keysof

Author: tisonkun

doc/Type/Hash.pod6

@@ -582,8 +582,8 @@ Defined as:
 
 Returns the type constraint for the keys of the invocant. For
 normal hashes the method returns the coercion type C<(Str(Any))>
-while for L<object hashes|/type/Hash#Object_hashes_and_type_constraints>
-the type used in the declaration of the C<Hash> is returned.
+while for L<non-string keys|/type/Hash#Non-string_keys>
+hashes the type used in the declaration of the C<Hash> is returned.
 
     my %h1 = 'apples' => 3, 'oranges' => 7;  # (no key type specified)
     say %h1.keyof;                           # OUTPUT: «(Str(Any))␤»
@@ -594,6 +594,10 @@ the type used in the declaration of the C<Hash> is returned.
     CATCH { default { put .^name, ': ', .Str } };
     # OUTPUT: «X::TypeCheck::Binding: Type check failed in binding to key; expected Str but got Int (3)␤»
 
+    my %h3{Int};                             # (this time, keys must be of type Int)
+    %h3{42} = 4096;
+    say %h3.keyof;                           # (Int)
+
 =head2 method of
 
 Defined as: