Bug: improve slack documentation

[gecube]

I tried to follow the next instructions: https://docs.coroot.com/alerting/slack/

Unfortunately, I failed. I was not able to find the mentioned sections on the slack site.

I think that I was confused by the instructions as it implicitly supposed that the first step is to find a proper section inside coroot interface (!)

I think this moment should be explicitly described (like open coroot interface, click there there and there).

Also it looks like that coroot interface was redesigned, so the proper place is:

settings -> then notifications -> and then configure button next to the slack word.