Good to have help link to FAQs or how-to on Special:ContentTranslation landing page. This can be close if we plan to move away from Special:ContentTranslation to Translation center in very near future.
The translatable user guide is at https://www.mediawiki.org/wiki/Help:Extension:ContentTranslation . This needs some designs for the right placement. This shouldn't depart too far from how it's implemented on other special pages, which have a "? Help" link at the top end corner (top right at https://www.mediawiki.org/wiki/Help:Extension:ContentTranslation , for example).