Add link to the Migrating the Ecosystem section

Author: biboudis

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

@@ -57,6 +57,8 @@ To run the community-build on a local machine from the main Dotty repository, fi
 submodules with `git submodule update --init` and run `sbt community-build/test`
 from the root of the dotty repo.
 
+For more details also follow the [Migrating the Ecosystem](https://www.scala-lang.org/2019/12/18/road-to-scala-3.html#migrating-the-ecosystem) on the Road to Scala 3 blogpost.
+
 ### New Issues
 
 Firstly thank you for all the hard work in issue reporting! Being feature complete means that our