Add release date for v0.20.1

Viktor Lövgren · Viktor Lövgren · commit 5f7e269578b9 · 2019-09-19T12:22:37.000+01:00
diff --git a/notes/0.20.1.markdown b/notes/0.20.1.markdown
@@ -14,3 +14,5 @@
 [#213]: https://github.com/ovotech/fs2-kafka/pull/213
 [#214]: https://github.com/ovotech/fs2-kafka/pull/214
 [#215]: https://github.com/ovotech/fs2-kafka/pull/215
+
+Released on 2019-09-19.
