Specify that this is optional

docs/webadministration.rst

@@ -159,7 +159,7 @@ You can add a fetched account by clicking on the `Add an account` button on the
 
 * Scan emails. When ticked, all the fetched emails will go through the local filters (rspamd, clamav, ...).
 
-* Folders. A comma separated list of folders to fetch from the server.
+* Folders. A comma separated list of folders to fetch from the server. This is optional, by default only the INBOX will be pulled.
 
 Click the submit button to apply settings. With the default polling interval, fetchmail will start polling the email account after ``FETCHMAIL_DELAY``.