DOC Document new config for splitting summary sentences (#428)

en/04_Changelogs/5.2.0.md

@@ -195,6 +195,7 @@ This will now fail by throwing an exception, which means your form won't render
 ### Other new features
 
 - A new [`SiteTree.hide_pagetypes`](api:SilverStripe\CMS\Model\SiteTree->hide_pagetypes) configuration property has been added. Unlike [`SiteTree.hide_ancestor`](api:SilverStripe\CMS\Model\SiteTree->hide_ancestor) (which has [now been deprecated](#api-silverstripe-cms)), this is an array. This allows you to define all page types that should be hidden in a single configuration property in your YAML configuration.
+- A new [`DBText.summary_sentence_separators`](api:SilverStripe\ORM\FieldType\DBText->summary_sentence_separators) configuration property has been added. This is used to split sentences in the [`DBText::Summary()`](api:SilverStripe\ORM\FieldType\DBText::Summary()) method. The default configuration value includes `.`, `!`, and `?`. Previously, only `.` was used to split sentences.
 - You can now upload [Braille ASCII file format](https://en.wikipedia.org/wiki/Braille_ASCII) (`.brf`) files to the CMS without needing to modify the [allowed file types](/developer_guides/files/allowed_file_types/).
 - The assets admin section now respects the [`Upload_Validator.default_max_file_size`](api:SilverStripe\Assets\Upload_Validator->default_max_file_size) configuration if [`AssetAdmin.max_upload_size`](api:SilverStripe\AssetAdmin\Controller\AssetAdmin->max_upload_size) has not been explicitly set for your project. Previously, asset admin would ignore `Upload_Validator.default_max_file_size` and just use the PHP `upload_max_filesize` ini configuration by default.