Add a Gitlab CI/CD section

[bellenot]

[bellenot]

@xkzl can you address the reviewer comments?

[meiyasan]

@xkzl can you address the reviewer comments?

@bellenot some issues pushing through your fork

$ git push
remote: Permission to bellenot/web.git denied to xkzl.
fatal: unable to access 'https://github.com/bellenot/web.git/': The requested URL returned error: 403

[bellenot]

@bellenot some issues pushing through your fork

$ git push
remote: Permission to bellenot/web.git denied to xkzl.
fatal: unable to access 'https://github.com/bellenot/web.git/': The requested URL returned error: 403

You can either suggest changes via the web interface, or post a diff, or a complete updated example. As you prefer

[meiyasan]

Here is the update I can offer.

# ROOT in Gitlab CI/CD (CERN)

Below are practical examples demonstrating how to integrate ROOT into a GitLab CI/CD instance, provided by one of our users on the [ROOT Forum](https://root-forum.cern.ch/t/gitlab-ci-using-root/57375/9).

## Using CVMFS

```yml #image:

your_task: stage: build script: - echo "CERN CVMFS repository" - ls -ls /cvmfs/sft.cern.ch/lcg/app/releases/ tags: - cvmfs ```

## Using Docker containers

```yml image: rootproject/root:latest

your_task: stage: build script: - echo -ne "ROOT Version " - which root - echo "ROOT Features" - root-config --features ```

[bellenot]

Thanks @xkzl ! Committed

[Axel-Naumann]

We need input from @martamaja10 / @vepadulano here - for me, showing these files is questionable because they basically just say "you can use cvmfs or rootproject/root:latest"; for the latter we already have https://root.cern/install/#run-in-a-docker-container

[martamaja10]

I think the use case is slightly different than just running ROOT purely from the Docker container, so I don't see why we shouldn't add it if it would spare some users installation time. I would maybe move it above the "from source" description as it would flow better to have all the docker/cvmfs together and the" from source" section at the end as it was?