Notification docs are not up to date

[armond-avanes]

Many new notifications have been recently added (e.g. Discord, Ntfy, Gotify, Slack, etc) which are not covered yet in the documentation.

UPDATE: Looks like alexjustesen/speedtest-tracker#1961 is going to affect this! You might want to settle on the final implementation of notifications (and whether you want to migrate to Apprise) before updating the docs.

[svenvg93]

Yes, we plan to update the notifications part once we finish the work on refactoring the notifications :)