SimpleDesk version: SimpleDesk 2.0 Anatidae and SimpleDesk 2.0.1
SMF version: SMF 2.0.11 and SMF 2.1 Beta 2
Latest revision from the GitHub. Download is of branch smf21 from 08.11.2015.
MySQLi version: 5.6.25
PHP: 5.6.11
2.1 Beta 2 is from the latest revision from the GitHub 08.11.2015
The configuration area Display Options are missing subtext in "Custom Fields for Tickets and Replie"
open root/Themes/default/sd_template/SimpleDesk-AdminCustomField.template.php
find
<dt><strong>', $txt['shd_admin_custom_fields_fieldtype'], ':</strong></dt>
replaces with
<dt><strong>', $txt['shd_admin_custom_fields_fieldtype'], ':</strong><br /><span class="smalltext">', $txt['shd_admin_custom_fields_description_desc'], '</span></dt>
Fixed in commit 5df98