Let Mix and MixHash have its own paragraph

Rewording it into a separate paragraph allows even easier skimming.

doc/Language/setbagmix.pod6

@@ -27,8 +27,11 @@ If you want to keep track of the B<number of times each object appeared>,
 you can use a L<Bag|/type/Bag> or L<BagHash|/type/BagHash>. In these
 Baggy containers each element has a weight (an unsigned integer)
 indicating the number of times the same object has been included in the
-collection. The types L<Mix|/type/Mix> and L<MixHash|/type/MixHash> are
-similar, but they also allow B<fractional weights>.
+collection.
+
+The types L<Mix|/type/Mix> and L<MixHash|/type/MixHash> are similar
+to L<Bag|/type/Bag> and L<BagHash|/type/BagHash>, but they also
+allow B<fractional weights>.
 
 =begin comment
 =defn  Bag or BagHash