docs: Update readme with info about ContainerGebSpec

README.md

@@ -5,8 +5,16 @@
 
 Geb Functional Testing for the Grails® framework.
 
+This plugin provides the Geb dependencies, a `create-functional-test` command for generating Geb tests in a Grails app
+and also adds a ContainerGebSpec that when inherited from automatically runs the browser in a container.
+
 This plugin provides the Geb dependencies and a `create-functional-test` command for generating Geb tests in a Grails app.
 
+It also provides a `ContainerGebSpec` class, which can be used in place of `GebSpec`, that automatically
+runs the browser in a container using [Testcontainers](https://java.testcontainers.org/). This requires a
+[compatible container runtime](https://java.testcontainers.org/supported_docker_environment/) such as
+[Docker](https://www.docker.com/) to be installed.
+
 For further reference please see the [Geb documentation](https://www.gebish.org).
 
 ## Examples