Added note about Docker experimental feature to README

README.md

@@ -131,6 +131,16 @@ $ cd ..
 In Itellij IDEA, create a new project using the `work` directory as the source.
 * File > New Project from Existing Sources > .../work > Maven
 
+## Docker
+We generally use Docker for testing. In order to reduce the size of images we also supply a squash option that collapses
+the layers in the image. This is a long-standing experimental feature that we have fould useful. However you will need
+to enable experimental features in your Docker Engine. 
+~~~
+{
+  "experimental": true,
+  "debug": true
+}
+~~~
 ## Branches
 As multiple projects have been combined, branch names use the ACS version they are targeting.
 For example the code used to create the repository in ACS 6.2.1 in a branch called `releases/6.2.1`.