Autorespond when labels are added

[adfoster-r7]

It would be great to add support for automatically commenting on a PR/issues when specific labels are added by maintainers. There's a great Github action that shows how this could work: https://github.com/peaceiris/actions-label-commenter

The use case is: Adding a label to a PR such as "needs-documentation", and a bot responding with what that entails to the contributor.

I've created a similar comment on the actions-label-commenter github action here - peaceiris/actions-label-commenter#24 (comment)

[kaxil]

That definitely looks like something we can add.

Hopefully I can get this over this Easter weekend.

Thanks for raising the issue.