Feedstock repo tags on publish

It would be great if the feedstock repos could be tagged with the full version number every time a recipe is published to conda-forge.

In particular, this would allow people to use the "Watch Releases" functionality in GitHub to be notified when a package is updated in conda-forge, and it would help with tracing between Anaconda.org, conda environments and the feedstocks.

What do you think? I assume it's straightforward to add to the scripts that push the artifacts to Anaconda.org, but it will presumably only affect each feedstock as it's re-rendered.