Document running Specter as a daemon

`--daemon` is broken, maybe we want to get rid of it instead of fixing it.
There are much better ways to make sure Specter is running and also started on system boot.
I started documenting usage of systemd in https://github.com/cryptoadvance/specter-desktop/pull/621, but we need similar manual for Mac (launchd?) and docker.
@nolimit1 made a great [docker image](https://github.com/lncm/docker-specter-desktop) for Specter, I think it makes sense to mention it in the docs somewhere as well.

Review the systemd usage documentation in pull request #621 and the existing Specter documentation first. Add comparable manual guidance for macOS launchd and Docker, including the linked docker-specter-desktop image, and clarify whether --daemon should be documented or removed.

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