Link to R2DevOps in gitlab doc

[nvuillam]

Test R2DevOps MegaLinter job and if it works as expected, add a link to R2DevOps in the doc

[coconux3]

Thank you for your time and consideration.

Megalinter opensource template is versioned and maintain by R2Devops community.
It allows users to upgrade Megalinter in their CI without copying/pasting YAML code anymore.
The template has been used more than 22k in GitLab-CI pipelines.
All versions are available here: https://r2devops.io/marketplace/gitlab/r2devops/hub/mega_linter

The community is curious about your feedback, of course open to any suggestion to fit expectations.