Tag github PRs using github tags to reflect its purpose

[chischaschos]

Possible purposes could be:

• Get early feedback
• Mark it as ready for final review
• Mark it as ready to be merged

etc

Thoughts?

[cone]

I think it's a good idea. In the past we have merged a PR that was a WIP because we assumed it was ready. That's why now we start the PR with "WIP" if it's not ready, but I think the tags are better.