Add documentation notes about use with Docker

Author: jonleighton

CHANGELOG.md

@@ -7,7 +7,8 @@
   impetus was to enable running a spring server inside a Docker
   container.
 * Numerous other tweaks to better support running Spring inside
-  containers
+  containers (see
+  https://github.com/jonleighton/spring-docker-example)
 
 ## 1.6.4
 

README.md

@@ -290,6 +290,13 @@ false
 So to avoid this problem, don't save off references to application
 constants in your initialization code.
 
+## Using Spring with a containerized development environment
+
+As of Spring 1.7, there is some support for doing this. See [this
+example
+repository](https://github.com/jonleighton/spring-docker-example) for
+information about how to do it with [Docker](https://www.docker.com/).
+
 ## Configuration
 
 Spring will read `~/.spring.rb` and `config/spring.rb` for custom