feat(org-mode): enable auto-fill-mode to automatically wrap lines at 80 characters

I've manually been enabling auto-fill-mode on a per buffer basis for a
long time, constantly forgetting to add it to my org-mode setup. Not
anymore :P

modules/org-mode/siren-org-mode.el

@@ -52,6 +52,7 @@
     (org-set-emph-re 'org-emphasis-regexp-components
                      org-emphasis-regexp-components)
 
+    (auto-fill-mode t)
     (siren-display-fill-column)
     (siren-display-indentation)
     (siren-display-line-numbers)