document the access tokens #572

in local.php
we have some values like

        'access_token_expire'  => 'P1D',
        'refresh_token_expire' => 'P1M',
        'auth_code_expire'     => 'PT10M',

Please add one comment line above each one with a short explanation and list some possible values , and a link to a php.net documentation what are those values

2. extend documentation for API to address those a abit