Add basic content to the gitlab section

docs/docker/gitlab-drupal-ci/index.md

+# Usage
+
+Register a runner with GitLab Runner and configure it like this:
+
+```
+[[runners]]
+  name = "DrupalCI"
+  url = "https://your.gitlab.url/"
+  token = "..."
+  executor = "docker"
+  [runners.docker]
+    tls_verify = false
+    image = "registry.lakedrops.com/docker/gitlab-drupal-ci:php-7.2"
+    privileged = true
+    disable_entrypoint_overwrite = false
+    oom_kill_disable = false
+    disable_cache = false
+    volumes = ["/var/run/docker.sock:/var/run/docker.sock", "/cache"]
+    shm_size = 0
+  [runners.cache]
+    [runners.cache.s3]
+    [runners.cache.gcs]
+```
+
+# Node version
+
+When using node from within this framework, this defaults to version `12-stretch-slim` but you can change the default version by setting the environment variable `NODE_VERSION` to one of these tags:
+
+- 8-jessie-slim
+- 10-jessie-slim
+- 12-stretch-slim
+- 13-stretch-slim
+
+# Credit
+
+- [Image from jonaskello](https://github.com/jonaskello/docker-and-compose)
+- [Alpine glibc from sgerrand](https://github.com/sgerrand/alpine-pkg-glibc)

docs/gitlab/ansible/index.md

+# Ansible
+
+Describe the templates for Ansible tasks in GitLab CI.

docs/gitlab/composer/index.md

+# Composer Packages
+
+Template for creating and updating composer packages in Gitlab.

docs/gitlab/drupal/index.md

+## Usage for test and deploy
+
+* You can set the CI/CD variable `COMPOSER_DOWNGRADE` to `1` for using the composer version 1. Default is composer version 2.
+* For authenticating with the Gitlab package repository, you have to set the variable `GITLAB_ACCESS_TOKEN`, which you have to create for the user who runs the pipeline.

mkdocs.yml

@@ -103,3 +103,6 @@ nav:
           - Zammad: ansible/roles/zammad/index.md
   - GitLab:
       - Home: gitlab/index.md
+      - Ansible: gitlab/ansible/index.md
+      - Composer: gitlab/composer/index.md
+      - Drupal: gitlab/drupal/index.md