Include contribution steps
What does this Merge Request do?
This MR adds explicit steps to the https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/master/CONTRIBUTING.md page to make it easier and more obvious for those looking to make contributions.
Merge Request checklist
- [-] Tests added for new functionality. If not, please raise Issue to follow-up.
-
This change is backward compatible. If not, please include steps to communicate to our users. -
Documentation added/updated, if needed. - [-]
gdk doctor
test added, if needed.