Better document how to config Play for containerized env

[octonato]

We should have better documentation for the PID file problem in Docker. The documentation is not so clear about it.

Relates to https://github.com/playframework/playframework/issues/9487

[wsargent]

It looks like the sbt-native-packager already deals with the PID issue mentioned

  // Since play uses separate pidfile we have to provide it with a proper path
  // name of the pid file must be play.pid
  s"-Dpidfile.path=/var/run/${packageName.value}/play.pid",

https://www.scala-sbt.org/sbt-native-packager/recipes/play.html#application-configuration

[wsargent]

Also https://medium.com/jeroen-rosenberg/lightweight-docker-containers-for-scala-apps-11b99cf1a666