use journald log driver in docker wrapper script

As mentioned in https://lwn.net/Articles/676831/, Docker's default loses the logs every time a container is destroyed. Also, https://docs.docker.com/config/containers/logging/configure/ says that the default never rotates the logfiles.

guide/install.md

@@ -52,6 +52,8 @@ common_docker_run_args=(
         --mount=type=bind,source=/var/lib/moonfire-nvr,destination=/var/lib/moonfire-nvr
         --user="$(id -u moonfire-nvr):$(id -g moonfire-nvr)"
         --security-opt=seccomp:unconfined
+        --log-driver=journald
+        --log-opt="tag=moonfire-nvr"
         --env=RUST_BACKTRACE=1
         --env=TZ=":${tz}"
 )