Add container deployment recipe to cookbook

[kraih]

As a followup to #1600, now that #1602 has been merged, we do still need a container recipe in the Deployment section of the cookbook. Not too detailed, mostly just explaining the Dockerfile you also get from ./myapp.pl generate dockerfile, but that also explains how to declare dependencies.

[kraih]

I've started a recipe, improvements would be very welcome. https://github.com/mojolicious/mojo/commit/9426d6fe3fa0966cafa221adcde596ef77f69e28

[kraih]

Perhaps a little Kubernetes too?