Add initial version of docker-compose.yml with gitlab-runner config

roboticsbuilder/docker-compose.yml

+version: '2'
+services:
+  gitlab-runner:
+    image: "gitlab/gitlab-runner:latest"
+    restart: always
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+      - /srv/gitlab-runner/config:/etc/gitlab-runner
+    network_mode: "bridge"
+    command: ["--debug", "run", "--user=gitlab-runner", "--working-directory=/home/gitlab-runner"]