Mention the Data paths documentation in the File class

This closes https://github.com/godotengine/godot-docs/issues/3799.

doc/classes/File.xml

@@ -20,6 +20,7 @@
 		    file.close()
 		    return content
 		[/codeblock]
+		In the example above, the file will be saved in the user data folder as specified in the [url=https://docs.godotengine.org/en/latest/tutorials/io/data_paths.html]Data paths[/url] documentation.
 	</description>
 	<tutorials>
 		<link>https://docs.godotengine.org/en/latest/getting_started/step_by_step/filesystem.html</link>