We also don't explain too much about systemd -- you're expected to find
out or know about that agnostically of this project.
Also some features that we don't really want to advertise super widely
are not worth mentioning here.
This allows avoiding having to delete after the fact for things like
issues #57 and #98.
Why have this over just stopping clipmenud? Well:
1. Stopping clipmenud should usually be an init system action, but we
are init-system agnostic. If we just exit, we don't have a way of
reliably starting again.
2. Even if we *do* do it using the init system, we don't want some
things (like a lingering xsel which owns the selection for
CM_OWN_CLIPBOARD) being killed as well.
3. This is a nicer interface for things like password managers to stop
clipmenu rather than stopping clipmenu entirely.
For privacy considerations, it's important to know about the max
clip option.
Users could also use a hint about how to cleanly override environment
variables with systemd.
