Add documentation on using Drupal VM for quick module/project demo environments via Docker

[geerlingguy]

Issue Type

• Documentation Report

Summary

Now that Drupal VM exists as a public Docker image, I've started integrating it with some of my contrib projects so I have a base/standardized environment to test in (which can be brought up in just seconds, which is important when I decide to do some contrib work, which eats up a lot of time per patch review).

I'm going to document this use case in the docs, since it's actually pretty easy to do, and you just need to know where to go to do it.

I might even add a script or something to make it easier/faster to build.

Anyways, this is probably closely related to #1390, #1388 and some other docker-related issues.