Motivate usage for Docker directly in documentation

Problem: I personally needed to understand Docker before I was able to find useful information, about Docker, in stack's documentation and blogs.

Context: As an exercise I'm deploying a simple web server in Haskell. My target platform was AWS Elastic Beanstalk. This required putting the application in a docker container. I reinvented the method in [docker-split-images](https://www.fpcomplete.com/blog/2015/12/docker-split-images) (poorly).

Opinions: Stack has very good support for deploying Haskell applications to services that support Docker. For developers that don't know what Docker is (me three weeks ago). It might help to give some examples deploying Haskell projects in ways that use Docker, directly in the documentation(rather then in a Docker sub section). There are certainly lots of useful examples [around](http://www.yesodweb.com/blog/2015/12/yesod-hosting-docker-kubernetes?__hstc=180777528.760e4080776ac254c5082e24fc5e62ec.1485462467164.1486140216480.1486400820329.6&__hssc=180777528.3.1486400820329&__hsfp=3282034609). The trick is finding and understanding them.

Let me know if this is an appropriate comment. I was encouraged to voice any confusion I may have.