Mention changes to examples in user guide
* **Breaking Change!** The task `DockerLoadImage` should use `Provider` type for image file
* **Breaking Change!** Use the default value `$buildDir/docker` for `DockerBuildImage.inputDir` to align with the default directory of the `Dockerfile` task
* **Breaking Change!** Align task names in `DockerJavaApplicationPlugin` with the ones from the `DockerSpringBootApplicationPlugin`
+* Examples in user guide that demonstrate the creation of a custom Docker task and the modification of existing `Dockerfile` instructions
[discrete]
=== v4.2.0 (December 16, 2018)
