Add note about yaml format options

website/site/content/docs/widgets.md

@@ -7,6 +7,8 @@ position: 30
 
 Widgets define the data type and interface for entry fields. Netlify CMS comes with several built-in widgets. Click the widget names in the sidebar to jump to specific widget details. We’re always adding new widgets, and you can also [create your own](https://www.netlifycms.org/docs/custom-widgets)!
 
+Widgets are specified as collection fields in the `config.yml` file. Note that [YAML syntax](https://en.wikipedia.org/wiki/YAML#Basic_components) allows lists and objects to be written in block or inline style, and the code samples below include a mix of both.
+
 To see working examples of all of the built-in widgets, try making a 'Kitchen Sink' collection item on the [CMS demo site](https://cms-demo.netlify.com). (No login required: click the login button and the CMS will open.) You can refer to the demo [configuration code](https://github.com/netlify/netlify-cms/blob/master/example/config.yml#L60) to see how each field was configured.