Send a message to #technoise about pending deploy as soon as a PR is merged

[evansd]

... along with a message about how to cancel the upcoming deploy.

This is what the old bot did and I found it quite useful.

[rebkwok]

@evansd Is this still relevant? I don't think OP deploys with a delay any more, so there's no point giving instructions about how to cancel, and it does post that it's starting the deploy.