fix b0rk link to systemd details

Author: dotysan

docs/automatic_start.md

@@ -44,4 +44,4 @@ Help with this would be greatly appreciated. Please get in touch.
 To enable automatic start with systemd:
 - Put `set -g @continuum-boot 'on'` in `.tmux.conf`
 - reload tmux config with this shell command: `$ tmux source-file ~/.tmux.conf`
-- see [systemd](./systemd_details.md) for more details about how this is implemented
+- see [systemd](/docs/systemd_details.md) for more details about how this is implemented