update docs/blog/_posts/2019-12-20-21th-dotty-milestone-release.md

Author: bishabosha

docs/blog/_posts/2019-12-20-21th-dotty-milestone-release.md

@@ -204,9 +204,11 @@ given [A,B]: (Show[A], Show[B]) => Show[(A,B)] =
   (a,b) => s"(${a.show}, ${b.show})"
 
 @main def ShowPair =
-  println((1 -> "one").show)
+  println((1 -> "one").show) // (1, "one")
 ```
 
+After a period of experimentation, either the new or old way will remain.
+
 ## New match syntax
 
 We introduce an improved treatment of `match`. We reintroduce `match` as an