Merge branch 'patch-1' into 'master'

update slack instructions

the previous instructions no longer apply, there is no "Incoming WebHooks" row anymore.

luckily there exists direct link to web hooks, so the previous steps aren't even neccessary

See merge request !3052

doc/integration/slack.md

@@ -2,19 +2,11 @@
 ## On Slack
-To enable Slack integration you must create an Incoming WebHooks integration on Slack;
+To enable Slack integration you must create an Incoming WebHooks integration on Slack:
 1.  [Sign in to Slack](https://slack.com/signin)
-1.  Select **Apps & Custom Integrations** from the dropdown next to your team name.
-
-1.  Click the **Configure** link (right-upper corner).
-
-1.  Select the **Custom integrations** tab.
-
-1.  Click the **Incoming WebHooks** row.
-
-1.  Click the **Add configuration** button.
+1.  Visit [Incoming WebHooks](https://my.slack.com/services/new/incoming-webhook/)
 1.  Choose the channel name you want to send notifications to.