Improve release documentation

Author: phxql

dev-doc/release.md

@@ -8,4 +8,8 @@ git commit -am "Release version $VERSION"
 git tag "v$VERSION"
 mvn versions:set -DgenerateBackupPoms=false -DnextSnapshot
 git commit -am "Start next development version"
+git push
+git push --tags
 ```
+
+Now attach the built JAR file to the [GitHub release](https://github.com/phxql/sonarqube-to-prometheus/releases).