Adds another example showing flattening slurpiness

As suggested by @CIAvash. Refs #2344

Author: JJ

doc/Type/List.pod6

@@ -216,6 +216,10 @@ But it behaves slurpily, inserting all arguments (after the first, which is the
 separator) into a single array
 
     say join('|', 3, 'þ', 1+4i);    # OUTPUT: «3|þ|1+4i␤»
+    say join ', ', <a b c>, 'd', 'e' , 'f'; OUTPUT: «a, b, c, d, e, f␤»
+
+In this case, the first list C«<a b c» is I<slurped> and flattened, unlike what
+happens when C<join> is invoked as a method.
 
 =head2 routine map