doom refresh -> doom sync

refresh isn't going anywhere, but sync will be the canonical command
here on out, because it is more appropriate for kind of work it will be
doing in the future.

core/cli/upgrade.el

@@ -11,7 +11,7 @@ following shell commands:
     cd ~/.emacs.d
     git pull --rebase
     bin/doom clean
-    bin/doom refresh
+    bin/doom sync
     bin/doom update"
   :bare t
   (let ((doom-auto-discard force-p))