loadZone method no longer exists; remove from README.md

[eporama]

Following along with the examples in the README.md file, the loadZone method no longer exists.

$zone = $api->loadZone($zoneId);
$zone_settings = $zone-> getSettings();

Seems like getSettings is directly on the ZoneApi class:

$zone_settings = $api->getZoneSettings($zoneId);