Document CircleCI setup_remote_docker

Author: mitjabez

docs/supported_docker_environment/continuous_integration/circle_ci.md

@@ -1,11 +1,51 @@
-# CircleCI (Cloud, Server v2.x, and Server v3.x)
+# CircleCI
 
-Your CircleCI configuration should use a dedicated VM for Testcontainers to work. You can achieve this by specifying the 
-executor type in your `.circleci/config.yml` to be `machine` instead of the default `docker` executor (see [Choosing an Executor Type](https://circleci.com/docs/2.0/executor-types/) for more info).  
+## CircleCI Cloud
+
+Testcontainers can be used on CircleCI with either the Docker executor or the Machine executor.
+
+When using the Docker executor, you must include the `setup_remote_docker` step to enable Docker support.
+
+Testcontainers will run containers using the Docker daemon provided by `setup_remote_docker`. Exposed container ports are automatically forwarded to the job container.
+
+Here’s a minimal CircleCI configuration using the Docker executor:
+
+
+```yaml
+version: 2.1
+jobs:
+  build:
+    docker:
+      - image: cimg/openjdk:23.0
+    steps:
+      - checkout
+      - setup_remote_docker
+      - run: mvn -B clean install
+```
+
+!!! warning
+    Testcontainers will map exposed container ports to the job container's network. However, due to the remote Docker architecture, **you should not assume containers are accessible via `localhost`**. Always use `.getHost()` and `.getMappedPort()` from Testcontainers to retrieve the correct hostname and port as described [here](/features/networking/#getting-the-container-host).
+
+Alternatively, you can use the Machine executor, which provides native Docker support without `setup_remote_docker`:
+
+```yaml
+version: 2.1
+jobs:
+  build:
+    machine:
+      image: ubuntu-2204:current
+    steps:
+      - checkout
+      - run: mvn -B clean install
+```
+
+## CircleCI Server
+
+On CircleCI Server, `setup_remote_docker` is not supported. To use Testcontainers, you must run your jobs on a dedicated virtual machine using the machine executor. You can configure this by specifying the executor type in your `.circleci/config.yml` to be `machine`. For more information see [Choosing an Executor Type](https://circleci.com/docs/executor-intro/).
 
 Here is a sample CircleCI configuration that does a checkout of a project and runs Maven:
 
-```yml
+```yaml
 jobs:
   build:
     # Check https://circleci.com/docs/executor-intro#linux-vm for more details
@@ -15,4 +55,3 @@ jobs:
       - run: mvn -B clean install
 ```
 
-You can learn more about the best practices of using Testcontainers together with CircleCI in [this article](https://www.atomicjar.com/2022/12/testcontainers-with-circleci/).