Merge pull request #121 from rspec/add-docker-note

Add docker note to readme

Author: JonRowe

README.md

@@ -5,16 +5,23 @@ Source for rspec.info.
 
 Requires a recent version of Ruby (> 2.1.x, tested on 2.5.3), bundler and imagemagick (to generate favicons).
 
-## Setup
+## Local Setup
 
-* `brew install imagemagick`
+* `brew install imagemagick` (or your package manager of choice).
 * `bundle install`
 * `middleman build`
 
-## Developing
+## Local Developing
 
+Run
 * `middleman server`
 
+## Docker Setup + Development
+
+If you don't have a local Ruby environment suitable to making changes to rspec.info,
+or prefer containerised development; you can find a 3rd party Docker image setup for
+this environment here: https://hub.docker.com/r/2performantirina/middleman-and-imagemagick/ 
+
 ## Deploying
 
 * `middleman deploy` (for http://rspec-staging.github.io/)