add content to the gapcursor page

docs/src/docPages/api/extensions/gapcursor.md

@@ -1,4 +1,7 @@
 # Gapcursor
+This extension loads the [ProseMirror Gapcursor plugin](https://github.com/ProseMirror/prosemirror-gapcursor) by Marijn Haverbeke, which adds a gap for the cursor in places that don’t allow regular selection. For example, after a table at the end of a document.
+
+Note that tiptap is renderless, but the dropcursor needs CSS for its appearance. The default CSS is added to the usage example below.
 
 ## Installation
 ```bash
@@ -9,15 +12,6 @@ npm install @tiptap/extension-gapcursor
 yarn add @tiptap/extension-gapcursor
 ```
 
-## Settings
-*None*
-
-## Commands
-*None*
-
-## Keyboard shortcuts
-*None*
-
 ## Source code
 [packages/extension-gapcursor/](https://github.com/ueberdosis/tiptap-next/blob/main/packages/extension-gapcursor/)