Mention borgmatic 1.8.9+ Apprise log sending capability.

[witten]

As part of this PR, I've removed an outdated (and incorrect) method for sending borgmatic's logs to Apprise and called out the new borgmatic 1.8.9 built-in approach.

Also: I haven't done it here, but I might suggest updating the docs to remove the old manual way for sending borgmatic logs to Apprise—or at least swapping the order so the new "native" way comes first. I'd be happy to do this if that's something you're interested in.