Replace user_config_dir by user_data_dir (#2105)

Author: alexkrz

book/src/todo_2.md

@@ -242,7 +242,7 @@ Filename: <a class=file-link href="https://github.com/gtk-rs/gtk4-rs/blob/main/b
 ```
 
 We plan to store our data as a file, so we create a utility function to provide a suitable file path for us.
-We use [`glib::user_config_dir`](https://gtk-rs.org/gtk-rs-core/stable/latest/docs/glib/fn.user_config_dir.html) to get the path to the config directory and create a new subdirectory for our app.
+We use [`glib::user_data_dir`](https://gtk-rs.org/gtk-rs-core/stable/latest/docs/glib/fn.user_data_dir.html) to get the path for storing application data and create a new subdirectory for our app.
 Then we return the file path.
 
 Filename: <a class=file-link href="https://github.com/gtk-rs/gtk4-rs/blob/main/book/listings/todo/2/utils.rs">listings/todo/2/utils.rs</a>