Add labels to existing issue

[ildella]

Hi. I did expect that

gh is 1111 -L "some label"

would add the label, but it does not.

[protoEvangelion]

That is a good use case which we do not currently offer.

Realistically, we should have an --update option here instead of only offering the ability to update the assignee.

I would be happy to work with you on how to add that and release the feature quickly. It is unlikely that I will get to this myself since I am working hard on getting v2.0 ready for release.