Enable "Server Informationen veröffentlichen" and set "Art der Gemeinschaftsseite" to "Globale Gemeinschaftsseite" on the admin page. Then activate the relay server:

$a->config['system']['relay_server'] = "https://relay.diasp.org";
$a->config['system']['relay_subscribe'] = true;
$a->config['system']['relay_scope'] = "all";

By enabling this your public posts will be distributed to the Diaspora relay system. And you will receive public postings from the relay servers. (They distribute content to all servers that are listed on the-federation.info)

After you done so (and you waited for a day) the community page will contain more stuff.