Configuring Slack for Prometheus

Go to slack.com and create a new workspace, following the step-by-step instructions on screen until you are given your workspace. Be sure to add a prometheus channel!
From your chat, use the workspace menu to go to Administration and then Manage apps.
Select Build on the top menu.
Press Start Building, then Create New App. Give your application a name, and then select the workspace you just created. Click Create App when done.
Select Incoming Webhooks from the menu.
Turn webhooks on.
Click Add New Webhook to Workspace, setting the channel name to the prometheus channel. Authorize the webhook.
Make note of the webhook URL.