Add example of ADTs with more than enums

[kubukoz]

The current example:

sealed trait Color
object Color {
  case object Red extends Color
  case object Green extends Color
  case object Blue extends Color
}

sealed trait Channel
object Channel {
  case object Alpha extends Channel
  case object Blue extends Channel
  case object Green extends Channel
  case object Red extends Channel
}

doesn't show that it's possible to transform if you have a more complex ADT with class leaves. That could be improved :)

[krzemin]

The example from tests can be used:

https://github.com/scalalandio/chimney/blob/master/chimney/src/test/scala/io/scalaland/chimney/examples/Shapes.scala

[MateuszKubuszok]

I think the current documentation covers this request :)