chore: Add duo-ui bottleneck to docs

What does this MR do?

When releasing a major gitlab-ui there is a duo-ui related temporary bottleneck 😐 This Issue has all the details around it: duo-ui#30 (closed)

This MR updates the gitlab-ui docs to make sure contributors are aware of the temporary hurdle and the workaround.

Once the docs are merged I will share this in the gitlab-ui slack channel to make sure contributors & maintainers are aware of it.