Add doom/homepage command

Not that the site exists yet, but I'm tired of having all these tidbits
of uncommitted code laying about. It'll exist eventually!

core/autoload/help.el

@@ -170,6 +170,12 @@ selection of all minor-modes, active or not."
           (goto-char location))
       (user-error "Aborted"))))
 
+;;;###autoload
+(defun doom/homepage ()
+  "Open the doom emacs homepage in the browser."
+  (interactive)
+  (browse-url "https://doomemacs.org"))
+
 ;;;###autoload
 (defun doom/help ()
   "Open Doom's user manual."