default base type for subset declaration

Author: k3ut0i

doc/Language/typesystem.pod6

@@ -911,6 +911,11 @@ Subsets can be used in signatures, e.g. by typing the output:
     a(1, "foo");  # passes
     a("foo", 1);  # fails
 
+If you skip the base type, it defaults to C<Any>. So the following two are equivalent:
+
+    subset A-or-B where * ~~ A | B
+    subset A-or-B of Any where * ~~ A | B
+
 Subsets can be anonymous, allowing inline placements where a subset is required
 but a name is neither needed nor desirable.