Needs documentation

[MalteJ]

Probably the builder_example repo should be included in this repo under a docs/example directory or something like this. I don't think it's a good idea to split the docs from the code.

[Vincinator]

I think we should provide a template repository that has all boilerplate code required for starting a new OS project with the gardenlinux/builder. This would look very similar to the previous builder_example.

Additionally, we need a getting started documentation. The documentation would reference the template repository.