We add an additional 'core' user service (i.e. one that gets loaded
before all others by turnstile) which populates the TURNSTILE_ENV_DIR
with all manner of custom set env vars that are important for other
applications.
Most importantly, this sets up the XDG directory compliance for
applications either managed by turnstile or applications started through
turnstile on my system. So, for example `pass` knows to search for its
database in `XDG_DATA_HOME` and river knows to search for binaries in a
PATH which has been prefixed with my custom user binary location.
Switching to runit (and turnstiled, which in turn activates user-local
runit service supervision) we can now have river run supervised by our
service manager quite easily.
We make use of this, but have to take care to export the
river-established wayland variables (DISPLAY, WAYLAND_DISPLAY) back into
the user environment for other processes since river will not be the
one responsible for spawning them anymore.
On finishing the service (i.e. exiting the process), we ensure
that the variables get removed from the environment again so it is not
polluted in the future.
Additionally, we load the (default for void runit) 'turnstile-ready'
service which can define core user services that need to exist before
others on login, and the session-local dbus service which river and
other programs will make use of. It is marked as essential with
turnstile-ready.
