Add docs for using Gitlab CI with Docker wormhole executor (#4770)

Author: JurrianFahner

docs/supported_docker_environment/continuous_integration/gitlab_ci.md

@@ -1,5 +1,36 @@
 # GitLab CI
 
+## Example using Docker socket
+This applies if you have your own GitlabCI runner installed, use the Docker executor and you have `/var/run/docker.sock` mounted in the runner configuration.
+
+See below for an example runner configuration: 
+```toml
+[[runners]]
+  name = "MACHINE_NAME"
+  url = "https://gitlab.com/"
+  token = "GENERATED_GITLAB_RUNNER_TOKEN"
+  executor = "docker"
+  [runners.docker]
+    tls_verify = false
+    image = "docker:latest"
+    privileged = false
+    disable_entrypoint_overwrite = false
+    oom_kill_disable = false
+    disable_cache = false
+    volumes = ["/var/run/docker.sock:/var/run/docker.sock", "/cache"]
+    shm_size = 0
+```
+
+Please also include the following in your GitlabCI pipeline definitions (`.gitlab-ci.yml`) that use Testcontainers:
+```yml
+variables:
+  TESTCONTAINERS_HOST_OVERRIDE: "host.docker.internal"
+```
+
+The environment variable `TESTCONTAINERS_HOST_OVERRIDE` needs to be configured, otherwise, a wrong IP address would be used to resolve the Docker host, which will likely lead to failing tests.
+
+## Example using DinD (Docker-in-Docker)
+
 In order to use Testcontainers in a Gitlab CI pipeline, you need to run the job as a Docker container (see [Patterns for running inside Docker](dind_patterns.md)).
 So edit your `.gitlab-ci.yml` to include the [Docker-In-Docker service](https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#use-docker-in-docker-workflow-with-docker-executor) (`docker:dind`) and set the `DOCKER_HOST` variable to `tcp://docker:2375` and `DOCKER_TLS_CERTDIR` to empty string.