Update README.md

Author: singerdmx

README.md

@@ -93,7 +93,7 @@ It is required to provide EmbedBuilder, e.g. [defaultEmbedBuilderWeb](https://gi
 
 ## Desktop
 
-It is required to provide application document directory for toolbar image button, e.g. [Sample Page](https://github.com/singerdmx/flutter-quill/blob/master/example/lib/pages/home_page.dart#L148).
+It is required to provide `filePickImpl` for toolbar image button, e.g. [Sample Page](https://github.com/singerdmx/flutter-quill/blob/master/example/lib/pages/home_page.dart#L149).
 
 ## Migrate Zefyr Data