update README to link to Scala 3 template

Author: SethTisue

README.md

@@ -1,12 +1,20 @@
-This is a [Giter8][g8] template for Scala.
+# Scala 2 seed template
+
+## Template usage
+
+This is a [Giter8][g8] template for Scala 2.
 
 ```
 sbt new scala/scala-seed.g8
 ```
 
-Template license
-----------------
-Written in 2016-2021 by Lightbend, Inc.
+## Looking for Scala 3 instead?
+
+That's over at https://github.com/scala/scala3.g8
+
+# Template license
+
+Written in 2016-2023 by Lightbend, Inc.
 
 To the extent possible under law, the author(s) have dedicated all copyright and related
 and neighboring rights to this template to the public domain worldwide.