Automation: add README on how to run tests

automation/README.Docker.md

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+# Running Automation in Docker
+
+## Prerequisites
+
+Before running the automation tests, ensure you have:
+
+* Docker and Docker Compose installed
+* Both `cloudberry-pxf` and `cloudberry` repositories cloned in the same parent directory (they will be mounted into the Docker container)
+
+## Running Automation Tests
+
+1. Navigate to the `cloudberry-pxf` directory:
+   ```bash
+   cd cloudberry-pxf
+   ```
+
+2. Stop and remove any existing containers and volumes:
+   ```bash
+   docker compose -f concourse/docker/pxf-cbdb-dev/ubuntu/docker-compose.yml down -v
+   ```
+
+3. Build the Docker images:
+   ```bash
+   docker compose -f concourse/docker/pxf-cbdb-dev/ubuntu/docker-compose.yml build
+   ```
+
+4. Start the containers in detached mode:
+   ```bash
+   docker compose -f concourse/docker/pxf-cbdb-dev/ubuntu/docker-compose.yml up -d
+   ```
+
+5. Run the entrypoint script to set up the environment:
+   ```bash
+   docker exec pxf-cbdb-dev bash -lc \
+      "cd /home/gpadmin/workspace/cloudberry-pxf/concourse/docker/pxf-cbdb-dev/ubuntu && ./script/entrypoint.sh"
+   ```
+
+6. Execute the test suite:
+   ```bash
+   docker exec pxf-cbdb-dev bash -lc \
+      "cd /home/gpadmin/workspace/cloudberry-pxf/concourse/docker/pxf-cbdb-dev/ubuntu && ./script/run_tests.sh"
+   ```
+   You can run tests multiple times in one container.
+
+## Troubleshooting
+When something went wrong:
+
+Jump into container: `docker compose ps` + `docker exec -it <id> bash`
+
+Check logs:
+
+* **PXF logs**: `/home/gpadmin/pxf-base/logs/`
+* **Hadoop logs**: `/home/gpadmin/workspace/singlecluster/storage/logs/`
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