Update CreateFileAsync and CreateFolderAsync descriptions

Depends on: <AvaloniaUI/Avalonia#20850>

Author: Frederisk

docs/concepts/services/storage-provider/storage-item.md

@@ -78,11 +78,11 @@ This method is lazily evaluate and is async.
 
 ### CreateFileAsync
 
-Creates a file with specified name as a child of the current storage folder
+Creates, or truncates and overwrites, a file with specified name as a child of the current storage folder.
 
 ### CreateFolderAsync
 
-Creates a folder with specified name as a child of the current storage folder
+Creates a folder with specified name as a child of the current storage folder unless they already exist.
 
 ## Extension methods
 
@@ -93,4 +93,4 @@ Android platform usually uses "content:" virtual file paths and Browser platform
 
 :::note
 If you want to save file path to reuse it later (in combination with TryGetFileFromPathAsync), please consider using [Bookmarks](./bookmarks) instead as they are designed to work in sandboxed environment, where user app might not have direct access to the physical file system.
-:::
+:::