Added dockerhub README.

Author: mwz

README_DOCKERHUB.md

@@ -0,0 +1,12 @@
+Docker images with out-of-the-box [SonarQube LTS](https://www.sonarqube.org) instance with support for [Scala](http://www.scala-lang.org), [Scoverage](https://github.com/scoverage/scalac-scoverage-plugin) (code coverage metrics) and [Scalastyle](http://www.scalastyle.org) + [Scapegoat](https://github.com/sksamuel/scapegoat) (static code analysis). :sunglasses:
+
+## Available versions
+- `2.2.1`, `latest` [Dockerfile](https://github.com/mwz/sonar-scala-docker/blob/master/2.1.0/Dockerfile), [(v2.2.1)](https://github.com/mwz/sonar-scala-docker/releases/tag/2.2.1)
+- `2.2.1-full` [Dockerfile](https://github.com/mwz/sonar-scala-docker/blob/master/2.2.1-full/Dockerfile), [(v2.2.1)](https://github.com/mwz/sonar-scala-docker/releases/tag/2.2.1)
+- `2.2.0` [Dockerfile](https://github.com/mwz/sonar-scala-docker/blob/master/2.2.0/Dockerfile), [(v2.2.0)](https://github.com/mwz/sonar-scala-docker/releases/tag/2.2.0)
+- `2.2.0-full` [Dockerfile](https://github.com/mwz/sonar-scala-docker/blob/master/2.2.0-full/Dockerfile), [(v2.2.0)](https://github.com/mwz/sonar-scala-docker/releases/tag/2.2.0)
+- `2.1.0` [Dockerfile](https://github.com/mwz/sonar-scala-docker/blob/master/2.1.0/Dockerfile), [(v2.1.0)](https://github.com/mwz/sonar-scala-docker/releases/tag/2.1.0)
+- `2.1.0-full` ([Dockerfile](https://github.com/mwz/sonar-scala-docker/blob/master/2.1.0-full/Dockerfile)), [(v2.1.0)](https://github.com/mwz/sonar-scala-docker/releases/tag/2.1.0)
+
+## Repository
+This project is open-sourced and can be found on [Github](https://github.com/mwz/sonar-scala-docker).