Add system-info Linux systemd user unit

Update the `system-info` directory with the addition of a `systemd`
service file and an new Linux script to display current CPU temperature
and core/thread utilization. Update `.conduit.yaml` with addition
`apt` dependencies `sysstat` and `jq`. Update the install and remove
scripts to setup and tear down the `systemd` user unit. Lastly, decrease
the `tmux` status line update interval from 5 to 2 seconds.

system-info/remove.sh

@@ -3,4 +3,7 @@
 if [ `uname` = Darwin ]; then
   launchctl unload ~/Library/LaunchAgents/system-info.plist
   rm ~/Library/LaunchAgents/system-info.plist
+else
+  systemctl --user stop system-info
+  systemctl --user disable system-info
 fi