This documentation is not using the current rendering mechanism and is probably outdated. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
The Page TSConfig which is normally stored in a field in the root page can be moved to the file Configuration/TSConfig/Page.ts .
In order to load this a line needs to be added to ext_tables.php :
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPageTSConfig( '<INCLUDE_TYPOSCRIPT: source="FILE:EXT:' . $_EXTKEY . '/Configuration/TSConfig/Page.ts">' );
Although the actual TSConfig could be included in ext_tables.php it's of course easier for maintenance to have it in a separate file.
In a similar way it's possible to load user TSConfig (