chore[emacs]: enable systemd layer

Enough with spacemacs complaining it should be installed

Author: kassick

dots/emacs/spacemacs.d/init.el

@@ -97,7 +97,7 @@ This function should only modify configuration layer settings."
    ;; `M-m f e R' (Emacs style) to install them.
    ;; ----------------------------------------------------------------
    dotspacemacs-configuration-layers
-   '(
+   '(systemd
      csv
      html
      (unicode-fonts :variables