Track releases in GitHub

[mraerino]

I noticed the releases on github are not in sync with the releases on pypy.
It would be less confusing, if there was a new tag on github pointing to the head commit of the release every time a release is deployed to pypy.

[sylvinus]

Yes we should, this will be done for all post-1.0 releases.

[sylvinus]

Do a "how to cut a release" doc