pingu lets you know when your process finishes.
It'll run on any POSIX system with
curl -Lo /usr/local/bin/pingu https://raw.githubusercontent.com/hoffa/pingu/master/pingu chmod +x /usr/local/bin/pingu
You'll need to create an Incoming Webhook and pass the URL to
pingu using the
SLACK_WEBHOOK_URL environment variable. Or you can just
export the variable during shell initialization.