Each element in an extension can be formatted as either plain text (.txt) or HTML. This includes the extension itself, along with any entities, widgets, and other resources bundled in the extension.
An extension readme file can be added in the extension directory structure (at the top level) to give further detailed information on the extension. In the case of a widget, this can provide further details on using the widget and could be displayed in the Design tab in a separate tab in the Widget Code View.
Note: None of the widgets included with Oracle Commerce Cloud Service use readme files, so adding them is optional.