Update README.md (scala#46)

Author: SethTisue

README.md

@@ -2,6 +2,14 @@
 
 scala-continuations is a library and a compiler plugin for Scala language that provides support for CPS transformations.
 
+You may also be interested in https://github.com/scala/scala-async, which covers what was once the most common use case for the continuations plugin.
+
+## Maintenance
+
 This library is community-maintained. The lead maintainer is [@danslapman](https://github.com/danslapman). 
 
-You may also be interested in https://github.com/scala/async, which covers the most common use case for the continuations plugin.
+## Scala versions supported
+
+The current development branch supports Scala 2.11 and 2.12.
+
+Volunteers are needed to [add support for Scala 2.13](https://github.com/scala/scala-continuations/issues/37).