chore(file-input): update readme to reflect current implementation

stories/info/atoms/fileInput.md

@@ -1,3 +1,11 @@
 # FileInput
 
-This is a Button with a hidden file input. When the button is clicked a file dialog appears and when a file is selected, the File instance is passed to the onChange handler. It can be used to build form components with.
+This is a `Button` with a hidden file input. When the button is clicked a file dialog appears and when a file is selected, the input's `FileList` instance is passed to the onChange handler. For security reasons, you cannot programmatically set a value to a file input. As a consequence of this, this component is not strictly speaking a "controlled input". There is no `value` prop because you simply cannot set it.
+
+## FileInput.SelectedFile
+
+This is a component that can be placed below the `FileInput` to show a list of files that have been selected locally, or have been uploaded before. When the `loading` prop is set to `true`, this component will show a loading icon and a "cancel" link. If `loading` is set to `false`, it will show a paperclip icon and a "remove" link.
+
+## FileInput.PlaceHolder
+
+A styled paragraph that you can place below the `FileInput` when no files have been selected yet.