Release notes for 2.0.0-M1

Kept it fairly short, I think it doesn't make sense to have an
exhaustive list but we should collect some of the highlights when
we get closer to a non-milestone 2.0.0 release.

Author: raboof

docs/src/main/paradox/release-notes/index.md

@@ -4,6 +4,7 @@
 
 @@@ index
 
+* [2.0 Milestone Releases](releases-2.0.md)
 * [1.3 Releases](releases-1.3.md)
 * [1.2 Releases](releases-1.2.md)
 * [1.1 Releases](releases-1.1.md)

docs/src/main/paradox/release-notes/releases-2.0.md

@@ -0,0 +1,17 @@
+# Release Notes (2.0.x)
+
+Apache Pekko 2.0.x releases support Java 17 and above.
+
+## 2.0.0-M1
+
+This is milestone release and is aimed at testing this new major version
+by early adopters. This is experimental. This release should not be used in production.
+
+### Main changes
+
+* Java 17 is the new minimum
+* Scala 2.12 support dropped
+* A lot of deprecated code removed
+* A lot of pekko.util classes for Scala version compatibility have been removed
+* Big change for all Java DSL users due to the removal of `pekko.japi.Function` (and related classes) to use `pekko.japi.function.Function` instead (lambdas should recompile ok but if you declared variables or functions explicitly, then you may need to change your imports)
+